Answers

2016-04-13T23:41:15+05:30
I dont know sorryyy........
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2016-04-14T12:21:42+05:30
 \frac{cos 20- sin20}{cos 20 + sin 20}

 \frac{cos 20(1- \frac{sin20}{cos20}) }{cos 20(1 +  \frac{sin20}{cos20} }

\frac{cos 20(1- tan20) }{cos 20(1 + tan20) }

\frac{1- tan20 }{1 + tan20 }

since, \frac{1- tan\alpha  }{1 + tan \alpha }= tan (45 -\alpha)

\frac{1- tan20 }{1 + tan20 } = Tan(45 - 20) = Tan 25

Hence proved

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