Penjelasan dengan langkah-langkah:

Sin (A+B)= sinA cosB + cosA sinB

sin 2x = sinxcosx + cosx sinx

= 2sinxcosx

soal

sin2x = cosx

2sinxcosx=cosx

2sinx = 1

sin x = 1/2

x = 30⁰

x = 30⁰x= 150⁰ di kuadran 2

b.

RUMUS

cos(a+b)=cosacosb-sinasinb

cos2x=cosxcosx-sinxsinx

=cos²x-sin²x

RUMUS

sin²x=1-cos²x

cos 2x=cos²x-sin²x

=cos²x-(1-cos²x)

=2cos²x -1

SOAL

cos x =cos2x

cosx=2cos²x-1

2cos²x-cosx-1 =0

cos²x-1/2 cosx-1/2=0

(cosx -1)(cosx +1/2)=0

cosx=1 dan cosx = -1/2

x=0⁰atau 360⁰ dan x= 120⁰atau240⁰