I'm so lost with this question:
If $\displaystyle y = x^2 + 4x$ and dx/dt = 10 find dy/dt when x = 5.
Can someone help me with this question please?
$\displaystyle \frac{d}{dt}(y = x^2 + 4x)$
$\displaystyle \frac{dy}{dt} = 2x\frac{dx}{dt} + 4\frac{dx}{dt}$
$\displaystyle \frac{dy}{dt} = \frac{dx}{dt}(2x+4)$
substitute in your given values for $\displaystyle x$ and $\displaystyle \frac{dx}{dt}$ to find the value for $\displaystyle \frac{dy}{dt}$