Biết \(\cos\left(a-\dfrac{b}{2}\right)=\dfrac{1}{2};\sin\left(a-\dfrac{b}{2}\right)>0;\sin\left(\dfrac{a}{2}-b\right)=\dfrac{3}{5};\cos\left(\dfrac{a}{2}-b\right)>0\) thì \(\cos\left(a+b\right)\) bằng
\(\dfrac{24\sqrt{3}-7}{50}\).\(\dfrac{7-24\sqrt{3}}{50}\).\(\dfrac{22\sqrt{3}-7}{50}\).\(\dfrac{7-22\sqrt{3}}{50}\).Hướng dẫn giải:
