$430$

Chapter $5$ Techniques of Integration

$81.$ Consider the fanction $f(x)=xcos2x.$

$82.$

$($a$)$ Find the signed area between the graph of $f(x)$ and the $x-$axis on $0,3\frac{}{4}$ shown in the figure next at the left.

$($b$)$ Find the area between the graph of $f(x)$ and the graph of $g(x)=-cos2x$ on $0,3\frac{}{4}$ shown in the figure next at the right.

Applications