<p>Please explain # 16 on Pg 807 in the blue book. Thanks.</p>
<p>x^2y - xy^2 = xy(x - y) </p>
<p>xy = 7
x - y = 5</p>
<p>7 * 5 = 35</p>
<p>D</p>
<p>He factored out xy incase you didn’t know what he did.</p>
<p>Or if you have a ti-89 (I really think a calc like the 89 shouldn’t be allowed but whatever) you could do:</p>
<p>solve(x*y=7 and x-y=5,x)</p>
<p>When it gives you x and y, you could just substitute them into x^2y-xy^2 and get your answer. Its more painful than the above method but another option if you have a calculator with a Computer Algebra System.</p>