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Explanation:
See the diagram below.
x+y = 2 is the same as y = 2-x
f(x) = x^2 and g(x) = 2-x intersect at (1,1) which is where we split the integrals so we have two regions to worry about
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[tex]\displaystyle \int_{0}^{1}x^2dx[/tex] shown in red in the diagram represents the area under y = x^2 from x = 0 to x = 1
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[tex]\displaystyle \int_{1}^{2}(2-x)dx[/tex]shown in blue (same diagram) represents the area under y = 2-x from x = 1 to x = 2.
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Combining the two integrals gets us the total area bounded by