text: class Formula {
      constructor(page) {
          this.page = page;
          this._text = document.querySelector('.content__text');
          this._formula = document.querySelector('.formula');
          this._arrowAX = this._formula.querySelector('.formula__arrow-ax');
          this._arrowAY = this._formula.querySelector('.formula__arrow-ay');
          this._arrowBX = this._formula.querySelector('.formula__arrow-bx');
          this._arrowBY = this._formula.querySelector('.formula__arrow-by');
          this._bottonGroup = document.querySelector('.button-group');
          this._buttonNext = this._bottonGroup.querySelector('.button-group__next');
          this._buttonBack = this._bottonGroup.querySelector('.button-group__back');
          this._buttonRefresh = this._bottonGroup.querySelector('.button-group__refresh');
          this._paginator = this._bottonGroup.querySelector('.button-group__paginator');
          this._secondEqual = this._formula.querySelector('.formula__second-equal');
          this._secondA = this._formula.querySelector('.formula__second-a');
          this._secondX = this._formula.querySelector('.formula__second-x');
          this._firstPlus = this._formula.querySelector('.formula__first-plus');
          this._firstPoints = this._formula.querySelector('.formula__first-points');
          this._thirdA = this._formula.querySelector('.formula__third-a');
          this._secondY = this._formula.querySelector('.formula__second-y');
          this._secondPlus = this._formula.querySelector('.formula__second-plus');
          this._secondPoints = this._formula.querySelector('.formula__second-points');
          this._secondB = this._formula.querySelector('.formula__second-b');
          this._thirdX = this._formula.querySelector('.formula__third-x');
          this._thirdPlus = this._formula.querySelector('.formula__third-plus');
          this._thirdPoints = this._formula.querySelector('.formula__third-points');
          this._thirdB = this._formula.querySelector('.formula__third-b');
          this._thirdY = this._formula.querySelector('.formula__third-y');
      }
  
      update(page) {
          if (page === 1) {
              this._buttonBack.style.display = 'none';
              this._text.style.color = '#fff';
              this._buttonRefresh.style.display = 'none';
              this._buttonNext.style.display = 'block';
              this._arrowAX.classList.remove('formula__arrow-ax_show');
              this._arrowAY.classList.remove('formula__arrow-ay_show');
              this._arrowAY.classList.remove('formula__arrow-ay_show-reverse');
              this._arrowBX.classList.remove('formula__arrow-bx_show');
              this._arrowBX.classList.remove('formula__arrow-bx_show-reverse');
              this._arrowBY.classList.remove('formula__arrow-by_show');
              this._arrowBY.classList.remove('formula__arrow-by_show-reverse');
              this._secondA.classList.remove('formula__second-a_show-reverse');
              this._secondA.classList.remove('formula__second-a_show');
              this._secondA.classList.remove('formula__second-x_show-reverse');
              this._secondX.classList.remove('formula__second-x_show');
              this._firstPlus.classList.remove('formula__first-plus_show');
              this._secondEqual.classList.remove('formula__second-equal_show');
              this._thirdA.classList.remove('formula__third-a_show-reverse');
              this._thirdA.classList.remove('formula__third-a_show');
              this._secondY.classList.remove('formula__second-y_show-reverse');
              this._secondY.classList.remove('formula__second-y_show');
              this._secondPlus.classList.remove('formula__second-plus_show');
              this._secondB.classList.remove('formula__second-b_show-reverse');
              this._secondB.classList.remove('formula__second-b_show');
              this._thirdX.classList.remove('formula__third-x_show-reverse');
              this._thirdX.classList.remove('formula__third-x_show');
              this._thirdPlus.classList.remove('formula__third-plus_show');
              this._thirdB.classList.remove('formula__third-b_show');
              this._thirdY.classList.remove('formula__third-y_show');
          } else if (page === 2) {
              this._buttonBack.style.display = 'block';
              this._arrowAX.classList.add('formula__arrow-ax_show');
              this._secondEqual.classList.remove('formula__second-equal_show');
              if (this._secondA.classList.contains('formula__second-a_show')) {
                  this._secondA.classList.remove('formula__second-a_show');
                  this._secondA.classList.add('formula__second-a_show-reverse');
              }
              if (this._secondX.classList.contains('formula__second-x_show')) {
                  this._secondX.classList.remove('formula__second-x_show');
                  this._secondX.classList.add('formula__second-x_show-reverse');
              }
              this._firstPlus.classList.remove('formula__first-plus_show');
              this._firstPoints.classList.remove('formula__first-points_show');
          } else if (page === 3) {
              this._secondEqual.classList.add('formula__second-equal_show');
              if (this._secondA.classList.contains('formula__second-a_show-reverse')) {
                  this._secondA.classList.remove('formula__second-a_show-reverse');
              }
              if (this._secondX.classList.contains('formula__second-x_show-reverse')) {
                  this._secondX.classList.remove('formula__second-x_show-reverse');
              }
              this._secondA.classList.add('formula__second-a_show');
              this._secondX.classList.add('formula__second-x_show');
              this._firstPlus.classList.add('formula__first-plus_show');
              this._firstPoints.classList.add('formula__first-points_show');
              if (this._arrowAY.classList.contains('formula__arrow-ay_show')) {
                  this._arrowAY.classList.remove('formula__arrow-ay_show')
                  this._arrowAY.classList.add('formula__arrow-ay_show-reverse');
              }
          } else if (page === 4) {
              if (this._arrowAY.classList.contains('formula__arrow-ay_show-reverse')) {
                  this._arrowAY.classList.remove('formula__arrow-ay_show-reverse');
              }
              this._arrowAY.classList.add('formula__arrow-ay_show');
              this._firstPoints.classList.add('formula__first-points_show');
              if (this._thirdA.classList.contains('formula__third-a_show')) {
                  this._thirdA.classList.remove('formula__third-a_show');
                  this._thirdA.classList.add('formula__third-a_show-reverse');
              }
              if (this._secondY.classList.contains('formula__second-y_show')) {
                  this._secondY.classList.remove('formula__second-y_show');
                  this._secondY.classList.add('formula__second-y_show-reverse');
              }
              this._secondPlus.classList.remove('formula__second-plus_show');
              this._secondPoints.classList.remove('formula__second-points_show');
          } else if (page === 5) {
              this._firstPoints.classList.remove('formula__first-points_show');
              if (this._thirdA.classList.contains('formula__third-a_show-reverse')) {
                  this._thirdA.classList.remove('formula__third-a_show-reverse');
              }
              if (this._secondY.classList.contains('formula__second-y_show-reverse')) {
                  this._secondY.classList.remove('formula__second-y_show-reverse')
              }
              this._thirdA.classList.add('formula__third-a_show');
              this._secondY.classList.add('formula__second-y_show');
              this._secondPlus.classList.add('formula__second-plus_show');
              this._secondPoints.classList.add('formula__second-points_show');
              this._arrowAY.classList.add('formula__arrow-ay_show');
              this._arrowAX.classList.add('formula__arrow-ax_show');
              if (this._arrowBX.classList.contains('formula__arrow-bx_show')) {
                  this._arrowBX.classList.remove('formula__arrow-bx_show');
                  this._arrowBX.classList.add('formula__arrow-bx_show-reverse');
              }
          } else if (page === 6) {
              this._arrowAY.classList.remove('formula__arrow-ay_show');
              this._arrowAX.classList.remove('formula__arrow-ax_show');
              if (this._arrowBX.classList.contains('formula__arrow-bx_show-reverse')) {
                  this._arrowBX.classList.remove('formula__arrow-bx_show-reverse');
              }
              this._arrowBX.classList.add('formula__arrow-bx_show');
              this._secondPoints.classList.add('formula__second-points_show');
              if (this._secondB.classList.contains('formula__second-b_show')) {
                  this._secondB.classList.remove('formula__second-b_show');
                  this._secondB.classList.add('formula__second-b_show-reverse');
              }
              if (this._thirdX.classList.contains('formula__third-x_show')) {
                  this._thirdX.classList.remove('formula__third-x_show');
                  this._thirdX.classList.add('formula__third-x_show-reverse');
              }
              this._thirdPlus.classList.remove('formula__third-plus_show');
              this._thirdPoints.classList.remove('formula__third-points_show');
          } else if (page === 7) {
              this._secondPoints.classList.remove('formula__second-points_show');
              if (this._secondB.classList.contains('formula__second-b_show-reverse')) {
                  this._secondB.classList.remove('formula__second-b_show-reverse')
              }
              this._secondB.classList.add('formula__second-b_show');
              if (this._thirdX.classList.contains('formula__third-x_show-reverse')) {
                  this._thirdX.classList.remove('formula__third-x_show-reverse');
              }
              this._thirdX.classList.add('formula__third-x_show');
              this._thirdPlus.classList.add('formula__third-plus_show');
              this._thirdPoints.classList.add('formula__third-points_show');
              if (this._arrowBY.classList.contains('formula__arrow-by_show')) {
                  this._arrowBY.classList.add('formula__arrow-by_show-reverse');
                  this._arrowBY.classList.remove('formula__arrow-by_show');
              }
          } else if (page === 8) {
              this._arrowBX.classList.add('formula__arrow-bx_show');
              if (this._arrowBY.classList.contains('formula__arrow-by_show-reverse')) {
                  this._arrowBY.classList.remove('formula__arrow-by_show-reverse');
              }
              this._arrowBY.classList.add('formula__arrow-by_show');
              this._thirdPoints.classList.add('formula__third-points_show');
          } else if (page === 9) {
              this._text.style.color = '#1A1B22';
              this._arrowBX.classList.remove('formula__arrow-bx_show');
              this._arrowBY.classList.remove('formula__arrow-by_show');
              this._thirdPoints.classList.remove('formula__third-points_show');
              this._thirdB.classList.add('formula__third-b_show');
              this._thirdY.classList.add('formula__third-y_show');
              this._buttonNext.style.display = 'none';
              this._buttonBack.style.display = 'none';
              this._buttonRefresh.style.display = 'block';
          }
          this._paginator.textContent = `${page} из 9`;
  
      }
  
  }
  
  export default Formula;