<p>Here are some “more difficult” problems where this last strategy is useful:</p>
<p>(1) If x+y=5 and z+w=7, then xz+xw+yz+yw=</p>
<p>(2) If rs=4, st=7, rt=63, and r>0, then rst=</p>
<p>(3) If x^15=2/z and x^14=2y/z which of the following is an expression for x in terms of y?</p>
<pre><code>(A) 3y
(B) 2y
(C) y
(D) 1/y
(E) 3/y
</code></pre>