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Tamil Nadu Board of Secondary EducationHSC Commerce Class 11

Show that tan-1(12)+tan-1(211)=tan-1(34) - Business Mathematics and Statistics

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Question

Show that `tan^-1 (1/2) + tan^-1 (2/11) = tan^-1 (3/4)`

Sum

Solution

We know that tan-1 x + tan-1 y = `tan^-1 ((x + y)/(1 - xy))`

Now LHS = `tan^-1 (1/2) + tan^-1 (2/11)`

`= tan^-1 ((1/2 + 2/11)/(1 - 1/2 xx 2/11))`

`= tan^-1 (((11 + 4)/22)/(1 - 1/11))`

`= tan^-1 ((15/22)/(10/11))`

`= tan^-1 (15/22 xx 11/10)`

`= tan^-1 ((3 xx 1)/(2 xx 2))`

`= tan^-1 (3/4)` = RHS

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Chapter 4: Trigonometry - Exercise 4.4 [Page 92]

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