Question

Prove that cos (60°_30°)=cos 60°cos 30°+sin 60° sin 30°•

Answer 1

Answer:

it is the double angle formula

Answer 2

i think all the sign should be positive

Step-by-step explanation:

cos(60+30)=cos60cos30-sin60sin30

cos(90)=cos60cos(90-60)-sin60sin(90-60)

cos90=cos60.sin60-sin60.cos60

cos90=0