Prove that Sec^4(1-sin^4)-2tan^2=1 using trigonometric identity

sec⁴A(1-sin⁴A)-2tan²A
=sec⁴A-sec⁴Asin⁴A-2tan²A
=sec⁴A-sin⁴A(1/cos⁴A)-2tan²A
=sec⁴A-tan⁴A-2tan²A
={(sec²A)²-(tan²A)²}-2tan²A
=(sec²A+tan²A)(sec²A-tan²A)-2tan²A
=sec²A+tan²A-2tan²A [∵, sec²A-tan²A=1]
=sec²A-tan²A
=1 (Proved)

 

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Arun (askIITians fpoum expert)