Question

please answer it's urgent​

Answer 1

Answer:

we know

cosx cosy - sinx siny = cos (x + y)

so

put x = 36 and y = 54

we get cos36 cos54 - sin36 sin54 = cos(36 + 54) = cos90 = 0

hence proved

Answer 2

Answer:

cos(36)=sin(90-36). (because costheta=sin(90-theta)

therefore cos36=sin 54

therefore cos36cos54=sin54cos54---i

now, similarly, sin36=cos(90-36). (because sintheta=cos(90-theta)

therefore sin36=cos 54

therefore sin36sin54=cos54sin54---ii

now subtract ii from i

= sin54cos54 - cos54sin54

= 0

hence proved

hope it helps:)