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Questions  

If p1,p2,p3 are respectively the perpendiculars from the vertices of a triangle to the opposite sides, then cosAp1+cosBp2+cosCp3 is equal to

a
1/r
b
1/R
c
1/Δ
d
none of these

detailed solution

Correct option is B

We have,cos⁡Ap1+cos⁡Bp2+cos⁡Cp3=12Δ(acos⁡A+bcos⁡B+icos⁡C)=RΔ(sin⁡Acos⁡A+sin⁡Bcos⁡B+sin⁡Ccos⁡C)=R2Δ(sin⁡2A+sin⁡2B+sin⁡2C)=R4sin⁡Asin⁡Bsin⁡C2Δ=2Rsin⁡Asin⁡Bsin⁡CΔ=2RΔ×2Δbc×2Δca×2Δab=16RΔ2a2b2c2=16RΔ2(4RΔ)2=1R

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