найдите эластичность функции f(x)=cos(-5x-5)/(4x^2-x-4) в точке а=-1

$E_y=\frac{x}{y}*y' \\\ y'=(\frac{cos(-5x-5)}{4x^2-x-4})'=(\frac{cos(5x+5)}{4x^2-x-4})'=\\\ =\frac{-5sin(5x+5)(4x^2-x-4)-cos(5x+5)(8x-1)}{(4x^2-x-4)^2}\\\ E_y=\frac{x(4x^2-x-4)}{cos(5x+5)}*\frac{-5sin(5x+5)(4x^2-x-4)-cos(5x+5)(8x-1)}{(4x^2-x-4)^2}=\\\ =\frac{x}{cos(5x+5)}*\frac{-5sin(5x+5)(4x^2-x-4)-cos(5x+5)(8x-1)}{4x^2-x-4}$

$E_y(-1)=\frac{-1}{cos0}*\frac{-5sin0*(-4)-cos0*(-9)}{1}=-1*9=-9$