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Question
Prove that:
`tan^-1 (4/3) + tan^-1 (1/7) = pi/4`
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Solution
LHS = `tan^-1 (4/3) + tan^-1 (1/7)`
`= tan^-1 ((4/3 - 1/7)/(1 + 4/3 * 1/7))`
`= tan^-1 ((28 - 3)/(21 + 4))`
`= tan^-1 (1) = pi/4` = RHS
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