wiː sˈʌbstɪtˌuːt ðɪs ˌɪntʊ ᵻkwˈeɪʒən ænd ɪkwˈeɪt ðə kˌoʊɪfˈɪʃənts bᵻlˈɔŋɪŋ tə ðə sˈeɪm fɹˈiːkwənsi, kˈiːpɪŋ ˈoʊnli ðə lˈoʊɪstˈɔːɹdɚ tˈɜːmz.
We substitute this into equation () and equate the coefficients belonging to the same frequency, keeping only the lowest-order terms.