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September 23, 2014

September 23, 2014

Posted by **Anand** on Saturday, January 26, 2013 at 2:19am.

- Maths -
**Damon**, Saturday, January 26, 2013 at 5:30amI assume you mean

cos^2 A + cos^2 B + cos^2 C

cos A = 0 this is a right triangle with right angle at A so cos^2 A =0

so

cos B = b/a

cos C = c/a

b = a cos B

c = a cos C

but b^2 + c^2 = a^2

a^2 cos^2 B + a^2 cos^2 C = a^2

so

cos^2 B + cos^2 C = 1

so

cos^2 A + cos^2 B + cos^2 C = 1

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