Question

Prove that: sin(x) sin(4x)=cos(x) cos(4x)​

Answer 1

Answer:

sinx+cosx=21

Squaring both sides,

sin2x+cos2x+2sinxcosx=41

1+2sinxcosx=41

sinxcosx=8−3..(i)

(sin2x+cos2x)(sin2x+cos2x)=1

sin4x+cos4x+2sin2xcos2x=1

sin4x+cos4x+2(8−3)2=1...From (i)

sin4x+cos4x+329=1

sin4x+cos4x=1−329

sin4x+cos4x

Step-by-step explanation:

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Answer 2

Answer:

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