In quadrilateral ABCD, the bisectors of angle A and angle B meet in a point P. If ∠C=105∘ and ∠D=55∘, find the measure of angle APB.
A
60∘
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B
70∘
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C
80∘
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D
90∘
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Solution
The correct option is C80∘ Given that, ∠C=105∘and∠D=55∘ We know that, ∠A+∠B+∠C+∠D=360∘ ⇒∠A+∠B+105∘+55∘=360∘ ⇒∠A+∠B=360∘−160∘ ⇒∠A+∠B=200∘ ⇒12∠A+12∠B=100∘ ...(i)
Since, AP and PB are the bisectors of ∠BADand∠ABC. Therefore, equation (i) can be written as, ⇒∠PAB+∠PBA=100∘ ...(ii)
In △APB, ∠PAB+∠PBA+∠APB=180∘ From (ii), 100∘+∠APB=180∘ ∠APB=80∘