Question

Найти наибольшее значение функции
y=28tgx-28+7π-4 на отрезке [ - π/4 ; π/4 ]

Answer 1

$y=28tgx-28x+7\pi -4\; \; ,\; \; x\in [-\frac{\pi}{4}\, ;\, \frac{\pi}{4}\, ]\\\\y'=\frac{28}{cos^2x} -28=28\cdot (\frac{1}{cos^2x}-1)=0\; \; \to \; \; cos^2x=1\; \; ,\; \; \frac{1+cos2x}{2}=1\; ,\\\\cos2x=1\; \; ,\; \; 2x=2\pi n\; ,\; \; x=\pi n\; ,\; n\in Z\\\\n=0\; \to \; x=0\in [-\frac{\pi}{4}\, ;\, \frac{\pi}{4}\, ]\\\\x=-\frac{\pi}{4}:\; \; y(-\frac{\pi}{4})=-28+7\pi +7\pi -4=14\pi -32\approx 11,96\\\\x=0:\; \; y(0)=7\pi -4\approx 17,98\\\\x=\frac{\pi}{4}:\; \; y(\frac{\pi}{4})=28-7\pi +7\pi -4=24$

$y_{naibol.}=y(\frac{\pi}{4})=24$