Question

Prove it cos^4 - sin^4 = cos2A

Answer 1

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$\bold{\underline{Question-}}$


Prove it cos^4 - sin^4 = cos2A


$\bold{\underline{Answer-}}$


LHS = cos^4 A - sin^4A

= (cos²A + sin²A) (cos²A - sin²A)

= 1(cos2A) [°•° cos²A + sin²A = 1]

= cos2A. [cos²A - sin²A = cos2A]


LHS = RHS

Answer 2

Answer:

Step-by-step explanation:

LHS = cos^4 A - sin^4A

= (cos²A + sin²A) (cos²A - sin²A)  

= 1(cos2A) [°•° cos²A + sin²A = 1]

= cos2A. [cos²A - sin²A = cos2A]

LHS = RHS

hence, prooved.