Evaluate the double integral. ∫∫ y sqrt(x^2-y^2) da, r={(x, y)|0≤y≤x, 0≤x≤1}. r. explain

First we will evaluate: ( substitution: u = x² - y²,  du = - 2 y dy )

= ( than plug in x and 0 )
= =
= 1/3 x³ ( then another integration )

= 1/3 * 1/4 = 1/12

40 & 50 in the right corner are the complementary angles as when placed in a sum (added together) they make 90°

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