Cho f(x) = sin^5 ax, a > 0. Tính f ' (pi)

* Hướng dẫn giải

Đáp án C

Ta có $f\text{'}\left(\mathrm{\pi }\right)=5{\sin }^4\left(a\mathrm{\pi }\right).a\cos \left(a\mathrm{\pi }\right)=5a{\sin }^{4}ax.\cos ax\Rightarrow f\text{'}\left(\mathrm{\pi }\right)=5a.{\sin }^4\left(a\mathrm{\pi }\right).\cos \left(a\mathrm{\pi }\right)$