In Δ ABC (a – b)2 cos2 2 c + (a + b)2 sin2 2 c =

Question

In Δ ABC \((a – b)^2 cos^2 \frac{c}{2} + (a + b)^2 sin^2 \frac{c}{2}=\) 

A) b² B) c² C) a² D) a² + b² + c²

Answer 1

Correct answer is C²

Instead of pythagoras You can use this formulas 

cos(C) = \(a^2 + b^2 − c^2\over 2ab\)