properties of triangles

If cos A + 2 cos Bcos A + 2 cos C =sin Bsin C
then prove that the triangle is isoceles or rt. angled.

1 Answers

1357

Manish Shankar ·2014-01-20 04:11:38

cosA*sinC+2cosBsinC=sinBcosA+2cosCsinB

=> cosA(sinB-sinC)=2(sinBcosC-cosBsinC)

=>cosA*2*cos[(B+C)/2]*sin[(B-C)/2]=2sin(B-C)

proceed from here

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