multiple choice 1 point\nthe function f has a continuous derivative. the table above gives values of f and…

multiple choice 1 point\nthe function f has a continuous derivative. the table above gives values of f and its derivative for x = 0 and x = 4. if ∫₀⁴f(x)dx = 8, what is the value of ∫₀⁴xf(x)dx?\n(a) -20 (b) -13 (c) -12 (d) -7 (e) 36
Answer
Answer:
D. -7
Explanation:
Step1: Apply integration - by - parts formula
The integration - by - parts formula is $\int_{a}^{b}u\mathrm{d}v=uv|{a}^{b}-\int{a}^{b}v\mathrm{d}u$. Let $u = x$ and $\mathrm{d}v=f^{\prime}(x)\mathrm{d}x$. Then $\mathrm{d}u=\mathrm{d}x$ and $v = f(x)$. So, $\int_{0}^{4}xf^{\prime}(x)\mathrm{d}x=xf(x)|{0}^{4}-\int{0}^{4}f(x)\mathrm{d}x$.
Step2: Evaluate $xf(x)|_{0}^{4}$
$xf(x)|_{0}^{4}=4f(4)-0\times f(0)$. From the table, $f(4)= - 3$ and $f(0)=2$. So, $4f(4)-0\times f(0)=4\times(-3)-0=-12$.
Step3: Substitute the value of $\int_{0}^{4}f(x)\mathrm{d}x$
We know that $\int_{0}^{4}f(x)\mathrm{d}x = 8$.
Step4: Calculate $\int_{0}^{4}xf^{\prime}(x)\mathrm{d}x$
$\int_{0}^{4}xf^{\prime}(x)\mathrm{d}x=xf(x)|{0}^{4}-\int{0}^{4}f(x)\mathrm{d}x=-12 - 8=-7$.