Question

Prove that in triangle ABC b²=a²+c²-2ca cosB

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Answer 1

Answer:

As we have ABC is a triangle hence a+b+c=0

So, a+b=−c

Squaring on both sides,

(a+b)(a+b)=(−c)(−c)

b2+a2+2abcos(π−C)=c2  [Using dot product ]

b2+a2+2ab(−cosC)=c2

c2=a2+b2−2abcosC

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