Question

In ΔABC, prove that 2(bc cos A + ca cos B + ab cos C) = a² + b² + c².

Answer 1

Answer:

2(bc cos A + ca cos B + ab cos C)

= a² + b² + c²

Step-by-step explanation:

Formula used:

Projection formula:

In any triangle ABC

1. a = b cosC+c cosB

2.b = c cosA+a cosC

3.c = a cosB+b cosA

2(bc cos A + ca cos B + ab cos C)

= 2bc cos A +2ca cos B + 2ab cos C

= bc cos A + ca cos B + ab cos C

+bc cos A + ca cos B + ab cos C

= a(b cosC + c cosB) + b(ccosA+acosC) +c(a cosB+b cosA)

=a(a)+b(b)+c(c)

= a² + b² + c².

I hope this answer helps you

Answer 2

Step-by-step explanation:

formula used is given above and problem answer also given

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