Question

how to prove this? ​

Answer 1

Answer:

here the formula is used cos(x+y)=

Step-by-step explanation:

cosx cos y -sinx siny .

here x=180/4-x, y=180/4-y. cos[(180/4-x)+ (180/4-y)]. cos[180/4+180/4-(x+y)]. cos180/2-(x+y). 180=π. cos[90°-(x+y)]. cos(90°-0°)=sin0°. sin(x+y). henced proved.