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Question

Mathematics Question on Trigonometric Functions

Given that p=tanα+tanβ,p = \tan \, \alpha+ \tan \, \beta, and q=cotα+cotβq = \cot \, \alpha + \cot \, \beta ; then what is (1p1q)\left( \frac{1}{p} - \frac{1}{q} \right) equal to ?

A

cot(αβ)\cot (\alpha - \beta)

B

tan(αβ)\tan (\alpha - \beta)

C

tan(α+β)\tan (\alpha + \beta)

D

cot(α+β)\cot (\alpha + \beta)

Answer

cot(α+β)\cot (\alpha + \beta)

Explanation

Solution

Since, p=tanα+tanβp = \tan \, \alpha + \tan \, \beta and q=cotα+cotβq = \cot \, \alpha + \cot \, \beta q=tanα+tanβq = \tan \, \alpha + \tan \, \beta q=1tanα+1tanβ=tanα+tanβtanαtanβ\Rightarrow q = \frac{1}{\tan\alpha} + \frac{1}{\tan\beta} = \frac{\tan\alpha + \tan\beta}{\tan\alpha \tan\beta} q=ptanαtanβq = \frac{p}{\tan\alpha \tan\beta} Hence , 1p1q=1ptanαtanβp\frac{1}{p} - \frac{1}{q} = \frac{1}{p} - \frac{\tan\alpha \tan\beta}{p} =1tanαtanβp= \frac{1- \tan\alpha \tan\beta}{p} =1tanαtanβtanα+tanβ=1tan(α+β)= \frac{1- \tan\alpha \tan\beta}{\tan\alpha + \tan\beta} = \frac{1}{\tan\left(\alpha+\beta\right)} =cot(α+β)= \cot \left(\alpha+\beta\right)