buktikan identitas trigonometri berikut. (sin x + cos x)(sin x + cos x) = 2 sin² x - 1

soal sepertinya di ralat seharusnya
(sin x + cos x)(sin x - cos x) = 2 sin² x - 1
= sin^2 x - Cos ^2 x
= Sin ^2 x - 1 - sin^2 x
= 2 sin ^2 x -1