Gimana nih ka pel.trigonometri

(i) sin 30 = 2 (sin 15)(cos 15)
[no. (i) BENAR]

sin (x + x) = (sin x)(cos x) + (cos x)(sin x)
sin 2x = 2 (sin x)(cos x)

Jadi, sin 30 = 2 (sin 15)(cos 15).

(ii) sin 30 = 2 (sin 15)(sin 45)
[no. (ii) jelas SALAH]

cos (x + x) = (cos x)(cos x) - (sin x)(sin x)
cos 2x = cos^2 x - sin^2 x
cos 30 = cos^2 15 - sin^2 15
[no. (v) BENAR]

INGaT
sin^2 A + cos^2 A = 1
=>> sin^2 A = 1 - cos^2 A
=>>cos^2 A = 1 - sin^2 A

Maka,
cos 2x = cos^2 x - (1 - cos^2 x)
cos 2x = 2 cos^2 x - 1


(iii) cos 30 = cos^2 15 + sin^2 15
tandanya harusnya (-)
[no. (iii) SALAH]

(iv) cos 30 = 2 cos^2 15 + sin^2 15
harusnya sin nya sudah diganti cos
[no. (iv) SALAH]

no. (v) BENAR

Jadi, pernyataan yg benar adalah (i) dan (v). Semoga membantu^^