Question #0eae5

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Answer 1 · 2017-11-09T07:28:19

See the proof below

The left hand side is

$LHS=(cos11+sin11)/(cos11-sin11)$

Divide numerator and denominator by $cos11$

$LHS=(cos11/cos11+sin11/cos11)/(cos11/cos11-sin11/cos11)$

$=(1+tan11)/(1-tan11)$

Since $tan45=1$

Therefore,

$LHS=(tan45+tan11)/(1-tan45tan11)$

We know that

$tan(a+b)=(tana+tanb)/(1-tanatanb)$

So,
$(tan45+tan11)/(1-tan45tan11)=tan56$

$=RHS$

$QED$