Cho \(\tan\alpha=m\). Khi đó \(\dfrac{a.\sin\alpha+b.\cos\alpha}{c.\sin\alpha+d.\cos\alpha}\) bằng
\(\dfrac{a+b}{c+d}m\).\(\dfrac{a+bm}{c+dm}\).\(\dfrac{am+b}{cm+d}\).\(\dfrac{a+b}{\left(c+d\right)m}\).Hướng dẫn giải:\(\dfrac{a.\sin\alpha+b.\cos\alpha}{c.\sin\alpha+d.\cos\alpha}=\dfrac{a.\dfrac{\sin\alpha}{\cos\alpha}+b}{c.\dfrac{\sin\alpha}{\cos\alpha}+d}=\dfrac{a.\tan\alpha+b}{c.\tan\alpha+d}=\dfrac{am+b}{cm+d}\)
