Question

cos4 A − sin4 A is equal to ……​

Answer 1

$Given \: cos^{4} A - sin^{4} A$

$= (cos^{2} A)^{2} - (sin^{2} A )^{2}$

$= (cos^{2} A + sin^{2} A) (cos^{2} A - sin^{2} A)$

$= 1 (cos^{2} A - sin^{2} A)$

$\boxed{ \pink{ \because cos^{2} A + sin^{2} A = 1 }}$

$= (cos^{2} A - sin^{2} A)$

$= cos 2A$

Therefore.,

$\red{ cos^{4} A - sin^{4} A}\green { = cos 2A}$

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Answer 2

Answer:

2cos^2a-1

Step-by-step explanation:

Identity used are

sin^2x+cos^2x=1