Question

# If in a triangle a = √3+1,b=√3−1,C=60∘ then the value of A is ?  75∘90∘105∘120∘

Solution

## The correct option is C 105∘A+B+C=180∘ A+B=120∘  .... (1) From law of tangent, we know that tan (A−B2)=a−ba+bcotC2 =(√3+1)−(√3−1)(√3+1)+(√3−1)cot30∘ =22√3cot30∘ tan(A−B2)=1 A−B=90∘  ..... (2) By equation 1 & 2, we get  A=105∘

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