The length $x$ of a rectangle is decreasing at the rate of $6$ cm/min and the width $y$ is increasing at the rate of $4$ cm/min. When $x=8$ cm and $y=4$ cm, the rate of change of the area of the rectangle is
Let $f(x) = \cos x$Differentiating with respect to $x$:$f'(x) = -\sin x$For a function to be strictly decreasing, $f'(x) < 0$:$-\sin x < 0$$\sin x > 0$The sine function is positive ($\sin x > 0$) in the first and second quadrants, specifically for the interval $x \in (0, \pi)$.
The derivative of $f(x,y)=x^2+xy$ at $P_0(1,1)$ in the direction of unit vector
$\vec{u}=\left(\frac{1}{\sqrt{2}}\right)\hat{i}+\left(\frac{1}{\sqrt{2}}\right)\hat{j}$
is
For continuity at $x=0$, need $\lim_{x\to 0^+} x^\alpha \log x = 0$
This holds when $\alpha > 0$ is not satisfied here, but by given condition extension works only at $\alpha = -1$