Area between f(x) = 20+x-x^2 and g(x) = x^2-5x over [1,3]

jwpaine

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Find area bounded by f(x) = 20 + x - x^2 and g(x) = x^2 - 5x over [1,3]

Since I will have to account for the negative area defined by g(x) = x^2 - 5x and y = 0, I will denote the area bounded by f(x) over [1,3] as A1 and g(x) over [1,3] as A2

A1 = \(\displaystyle \int_1^{3} 20 + x - x^2\,dx = \frac{106}{3}\)

A2 = \(\displaystyle \int_1^{3} x^2 - 5x = \frac{-34}{3}\)

But when I add these two areas together, I don't get the same answer as my book. My book says the answer to this problem is \(\displaystyle \frac{343}{3}\)

Any help would be appreciated. What am I doing wrong?
 
I'm pretty sure the answer in the book is incorrect given what you have.
 
\(\displaystyle A = \int_1^3 f(x) - g(x) dx = \int_1^3 20 + 6x - 2x^2 dx = \frac{140}{3}\)
 
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