Đáp án:
Giải thích các bước giải:
b)
$0\leq sin^23x\leq 1$
$0\leq 1-sin^23x\leq 1$
$0\leq \sqrt{1-sin^23x}\leq 1$
$-1\leq \sqrt{1-sin^23x}-1\leq 0$
Vậy $Min=-1$ khi $x=\dfrac{\pi}{6}+k\dfrac{2\pi}{3}$
$Max=0$ khi $x=\dfrac{k\pi}{3}$
c)$y=4sin^5x-7$
$-1\leq sin^5x\leq 1$
$-4\leq 4sin^5x\leq 4$
$-11\leq 4sin^5x-7\leq -3$
Vậy $Min=-11$ khi $x=\dfrac{-\pi}{2}+k2\pi$
$Max=-3$ khi $x=\dfrac{\pi}{2}+k2\pi$
