Question

sin⁴A—cos⁴A is equal to :

(A) 1
(B) 1—2cos²A
(c) 0
(D) tan²A

Answer 1

Sin⁴a - cos⁴a = (sin²a + cos²a)(sin²a - cos²a ) = 1(sin²a - cos²a) = (sin²a - cos²a) = (1 - cos²a - cos²a) = 1 - 2cos²a
answer is (b)

Answer 2

Option B is correct.

1-2cos²A


Solution:


sin⁴A - cos⁴A


(Sin²A)² - ( cos²A)²


[ (a²-b²)= (a+b) (a-b)


(Sin²A+cos²A) (Sin²A- cos²A)


1  × (1-cos²A- cos²A)


[ (Sin²A+cos²A)=1 , sin²A= 1-cos²A]


1-2cos²A

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Hope this will help you......