Answers

2014-11-04T18:14:00+05:30

tan2B=cot(B-18
 since
 tan(90-Ф)=cotФ
so
tan2B=tan(90-B+18)
so
2B=108-B
B=36
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2014-11-05T02:49:26+05:30

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Cot (B-18) = Tan (90 - (B - 18)) = Tan (108 - B)

Tan 2B = Tan (108 - B)   =>  there are multiple possibilities.
 
1)    2 B =  108 - B    =>    3 B = 108     =>   B = 36°

2)   2 B = 180 + 108 - B     =>    3 B = 288   =>  B = 96°
      or,  180 + 2B = 108 -B   =>  B = - 24°

 As 2B is an acute angle,  we choose only the 1st one.  B = 36°


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