Area between lines

Calculus Level 3

What is the area bound by the lines y = 2 x y=2\sqrt x , y = 3 y=3 , y = x 5 y=x-5 , x = 5 x=5 and x = 10 x=10 ?

Hint: Plotting these graphs may be helpful.

10 10.26 10.06 10.16

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1 solution

Zico Quintina
Jul 3, 2018

From the graph below, we can see that we just need to find the area between y = 2 x y = 2 \sqrt{x} and y = 3 y = 3 from x = 5 x = 5 to x = 10 x = 10 , and then subtract the area of the cross-hatched triangle, which is clearly 1 2 ( 2 ) ( 2 ) = 2 \frac{1}{2}(2)(2) = 2 .

So the area we're looking for is

5 10 ( 2 x 3 ) d x 2 = [ 4 3 x 3 3 x ] 5 10 2 = ( 40 10 3 30 ) ( 20 5 3 15 ) 2 = 40 10 20 5 3 17 10.26 \begin{array}{rl} \int_5^{10} (2\sqrt{x} - 3) \ dx - 2 &= \ \ \left[ \dfrac{4}{3} \sqrt{x^3} - 3x \right]_5^{10} - \ 2 \\ \\ &= \ \ \left( \dfrac{40 \sqrt{10}}{3} - 30 \right) - \left( \dfrac{20 \sqrt{5}}{3} - 15 \right) - \ 2 \\ \\ &= \ \ \dfrac{40 \sqrt{10} - 20 \sqrt{5} }{3} - 17 \\ \\ &\approx \ \ \boxed{10.26} \end{array}

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