CPM Homework Help : APCALC Problem 12-38

Multiple Choice: The function $f$ is continuous on the closed interval $[3, 9]$ and has values given in the table below.

$x$	$3$	$4$	$7$	$9$
$f\left(x\right)$	$50$	$40$	$20$	$30$

Using the subintervals $[3, 4]$ , $[4, 7]$ , and $[7, 9]$ , what is the trapezoidal approximation of $\int _ { 3 } ^ { 9 } f ( x ) d x$ ?

Hint:

Be careful! The subintervals have different widths.

Step:

$\frac{1}{2}(f(3)+f(4))\cdot1+\frac{1}{2}(f(4)+f(7))\cdot3+\frac{1}{2}(f(7)+f(9))\cdot2$