How to prove that 1-tan^2a/1+tan^2a=2cos^2a-1

can i get an answer as soon as possible like today,please?

tan = sin/cos

Multiply top and bottom by cos^2 a

(cos^2 a - sin^2 a)/(cos^2 a + sin^2 a)

[cos^2 + sin^2 = 1]

= cos^2 a - sin^2 a

= cos^2 a - (1 - cos^2 a)

= 2*cos^2 a - 1 <<<

1-tan^2a/1+tan^2a
we know that 1+tan^2a=sec^2a
so we get-
(1-tan^2a)/sec^2a
=cos^2a-sin^2=
2cos^2a-1
(as sin^2a=1-cos^2a)
hope it helped..

1-tan^2(a)/1+tan^2(a) =1-tan^2(a)/sec^2(a)
=cos^2(a)-sin^2(a)
=cos^2(a)-[1-cos^2(a)]=
2cos^2(a)-1

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