Question

Найдите:
а) f'(-2), если f(x) = (5+2x) ^4
б) f'(π), если f(x) = sin x / x

Answer 1

a)

$f(x) = {(5 + 2x)}^{4}$

$f'(x) = (( {(5 + 2x)}^{4})') \times (5 + 2x)'$

$f'(x) = 4 \times {(5 + 2x)}^{3} \times 2 = 8 \times {(5 + 2x)}^{3}$

$f'( - 2) = 8 \times {(5 + 2 \times ( - 2))}^{3} = 8 \times {(5 - 4)}^{3} = 8 \times {1}^{3} = 8$

б)

$f(x) = \frac{ \sin(x) }{x}$

$f'(x) = \frac{(( \sin(x))') \times x - (x)' \times \sin(x) }{ {x}^{2} }$

$f'(x) = \frac{ \cos(x) \times x - 1 \times \sin(x) }{ {x}^{2} }$

$f'(\pi) = \frac{ \cos(\pi) \times \pi - \sin(\pi) }{ {\pi}^{2} } = \frac{ - 1 \times \pi - 0}{ {\pi}^{2} } = - \frac{\pi}{ {\pi}^{2} } = - \frac{1}{\pi}$