Question

How do you prove 4 (cos^4A + sin^4A) / (3+cos4A) = (cos^4A-sin^4A) sec2A?​

Answer 1

Explanation:

Step 1: (sin²A+cos²A)²

Step 2: (a+b)² = a²+b²+2ab

Step 3: (sin²A+cos²A)²=sin⁴+cos⁴+2sin²Acos²A

make sure to use: sin²a+cos²a=1

Step 4: (1)²-2sin²Acos²A = sin⁴A+cos⁴A

Step 5: 1-2sin²Acos²A = sin⁴A+cos⁴A