Question

(1-sin(a))*(1+sin(a))+ cos²(a)-1= помогите пж

Answer 1

(1-sina)(1+sina)+cos²a-1=1-sin²a+cos²a-1=cos²a-sin²a=cos(2a)

(Formuli: (x-y)(x+y)=x²-y², cos2x=cos²x-sin²x)

Answer 2

$(1 - \sin(a) )(1 + \sin(a) ) + \cos {}^{2} (a) - 1 = \\ \\ ( {1}^{2} - \sin {}^{2} (a) ) + \cos {}^{2} (a) - 1 = \\ \\ (1 - \sin {}^{2} (a) ) + \cos {}^{2} (a) - 1 = \\ \\ \cos {}^{2} (a) + \cos {}^{2} (a) - 1 = \\ \\ 2 \cos {}^{2} (a) - 1 = \cos(2a)$