Area eh

Calculus Level 3

The area of the shaded region can be written as a b + e c 1 e \dfrac{a}{b} + \dfrac{e^{c}-1}{e} , where a a and b b are positive coprime integers. Find a + b + c a+b+c .


The answer is 21.

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1 solution

Chew-Seong Cheong
Jan 13, 2019

The area of the shaded region is given by:

A = 1 1 ( e y y 2 + 3 ) d y = e y y 3 3 + 3 y 1 1 = e 1 3 + 3 ( 1 e + 1 3 3 ) = 16 3 + e 2 1 e \begin{aligned} A & = \int_{-1}^1 \left(e^y - y^2 + 3\right) dy \\ & = e^y - \frac {y^3}3 + 3y \bigg|_{-1}^1 \\ & = e - \frac 13 + 3 - \left(\frac 1e + \frac 13 - 3\right) \\ & = \frac {16}3 + \frac {e^2-1}e \end{aligned}

Therefore, a + b + c = 16 + 3 + 2 = 21 a+b+c = 16+3+2 = \boxed{21} .

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