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प्रश्न
Prove the following identities, where the angles involved are acute angles for which the expressions are defined:
`((1+tan^2A)/(1+cot^2A))=((1-tanA)/(1-cotA))^2=tan^2A`
उत्तर
`((1+tan^2A)/(1+cot^2A))=((1-tanA)/(1-cotA))^2=tan^2A`
`(1+tan^2A)/(1+cot^2A)=(1+sin^2A/cos^2A)/(1+cos^2A/sin^2A)`
= `((cos^2A + sin^2A)/cos^2A)/((sin^2A + cos^2A)/sin^2A)`
= `(1/cos^2A)/(1/sin^2A)`
= `sin^2A/cos^2A`
= tan2A
`((1-tanA)/(1-cotA))^2=(1+tan^2A-2tanA)/(1+cot^2A-2cotA)`
= `(sec^2A-2tanA)/(cosec^2A-2cotA)`
= `(1/cos^2A-(2sinA)/cosA)/(1/sin^2A-(2cosA)/sinA)`
= `((1 - 2sinAcosA)/cos^2A)/((1 - 2sinAcosA)/sin^2A)`
= `sin^2A/cos^2A`
= tan2A
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