title: Multplication two inputs Angular
body: <p>I would like get values from 2 inputs (<strong>NUM_PRECIO_UNITARIO</strong> and <strong>NUM_PORCENTAJE_IVA</strong>) and show diamically the result of multplication in other input (<strong>NUM_VALOR_IVA</strong>) actually this is my html</p>
  
  <p>file.html</p>
  
  <pre><code>&lt;div class="form-group col-sm-5"&gt;
      &lt;mat-form-field&gt;                    
          &lt;input matInput type="number" formControlName="NUM_VALOR_IVA" placeholder="Valor IVA" value="{{formDetalleOC.get('NUM_PRECIO_UNITARIO').value * formDetalleOC.get('NUM_PORCENTAJE_IVA').value}}" required&gt;                  
      &lt;/mat-form-field&gt;
  &lt;/div&gt;  
  </code></pre>
  
  <p>file.ts</p>
  
  <pre><code>ngOnInit() {
      this.createControlItemOC
  } 
  
  createControlItemOC() {  
      this.formDetalleOC = this.fb.group({         
          NUM_PRECIO_UNITARIO: 0,
          NUM_PORCENTAJE_IVA: 0,   
          NUM_VALOR_IVA: 0,
      })  
  }
  </code></pre>
  
  <p>this is the result in the front </p>
  
  <p><a href="https://i.stack.imgur.com/Y7ayU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Y7ayU.png" alt="enter image description here"></a></p>
  
  <p>but in my form the value not change</p>
  
  <p><a href="https://i.stack.imgur.com/wQcZg.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wQcZg.png" alt="enter image description here"></a></p>