With usual notations prove that 2 (bc cos A +ac cos B + ab cos C = a^2 + b^2 +c^2
With usual notations prove that 2 (bc cos A +ac cos B + ab cos C = a^2 + b^2 +c^2
Samaira Shah , 8 Years ago
Grade 11
Trigonometry> With usual notations prove that 2 (bc cos...
1 Answers
Arun
Dear student
cos A = b² + c² -a²/ 2bc
Hencw
2bc cos A = b² +c² -a²
similarly
2bc cos B = a² + c² -b²
&
2bc cos C = a² + b² -c²
Now add all the three equations, you will get the desired result.
Regards
Arun(askIITians forum expert)
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