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

A) b^{2} B) c^{2} C) a^{2} D) a^{2} + b^{2} + c^{2}

Correct answer is C^{2}

Instead of pythagoras You can use this formulas

cos(C) = \(a^2 + b^2 − c^2\over 2ab\)