Question

Rút gọn:

\(\dfrac{2\cos^2\alpha-1}{\sin\alpha+\cos\alpha}\)

Answer 1

\(=\dfrac{2cos^2a-\left(sin^2a+cos^2a\right)}{sina+cosa}=\dfrac{cos^2a-sin^2a}{sina+cosa}=\dfrac{\left(cosa-sina\right)\left(cosa+sina\right)}{sina+cosa}=cosa-sina\)

Answer 2

\(\dfrac{2\cos^2\alpha-1}{\sin\alpha+\cos\alpha}\)

\(=\dfrac{2\cos^2\alpha-\sin^2\alpha-\cos^2\alpha}{\cos\alpha+\sin\alpha}\)

\(=\cos\alpha-\sin\alpha\)