Question

solve cos^4A-sin^4A
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Answer 1

Answer:

$\displaystyle \sf \bigstar \: \: \: \small{ \rm{ \green{ \underline{ { \cos }^{2} a - 1}}}}$

Step-by-step explanation:

$\displaystyle \sf ({ \cos }^{4} a - { \sin}^{4}a ) \: = ({ \cos}^{2} a \: - { \sin }^{2} a)( { \cos}^{2} a + { \sin}^{2} a) \: \: \: \: \: \: \: \: \\ \\ = \displaystyle \sf({ \cos}^{2} a \: - { \sin }^{2} a)(1) \\ \\ = \: \displaystyle \sf{ \cos}^{2} a - 1 - { \cos }^{2} a \\ \\ \displaystyle \sf = 2 { \cos }^{2}a - 1 \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \:$