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महाराष्ट्र राज्य शिक्षण मंडळएचएससी विज्ञान (सामान्य) इयत्ता १२ वी

If | x | < 1, then prove that x2xx2xxxx2tan-1x=tan-1(2x1-x2)=sin-1(2x1+x2)=cos-1(1-x21+x2) - Mathematics and Statistics

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प्रश्न

If | x | < 1, then prove that

`2 tan^-1 "x" = tan^-1 ("2x"/(1 - "x"^2)) = sin^-1 ("2x"/(1 + "x"^2)) = cos^-1 ((1 - "x"^2)/(1 + "x"^2))`

बेरीज
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उत्तर

Let tan-1x = y

Then, x = tan y

Now, `tan^-1 ("2x"/(1 - "x"^2)) = tan^-1  (("2 tan y")/(1 - tan^2 "y"))`

`= tan^-1 (tan 2"y")`

= 2y

= 2 tan-1x         ......(1)

`sin^-1 ("2x"/(1 + "x"^2)) = sin^-1 (("2 tan y")/(1 + tan^2 "y"))`

`= sin^-1 (sin 2"y")`

= 2y

= 2 tan-1x         ......(2)

`cos^-1 ((1 - "x"^2)/(1 + "x"^2)) = cos^-1 ((1 - tan^2 "y")/(1 + tan^2 "y"))`

`= cos^-1 (cos "2y")`

= 2y

`= 2 tan^-1 "x"`        ......(3)

From (1), (2) and (3), we get

`2 tan^-1 "x" = tan^-1 ("2x"/(1 - "x"^2)) = sin^-1 ("2x"/(1 + "x"^2)) = cos^-1 ((1 - "x"^2)/(1 + "x"^2))`

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