#20 (no calculator) from test 10

#20 (no calculator) from test 10

This is a difference of two squares question: you have to remember that $u^2-t^2$ factors to $(u+t)(u-t)$ .

Armed with that fact, you can rewrite what the question is asking for:

$(u-t)(u^2-t^2)=(u-t)(u+t)(u-t)$

And now all you need to do is plug in the values you’re given: $u+t=5$ and $u-t=2$ .

$(u-t)(u^2-t^2)=(u-t)(u+t)(u-t)=(2)(5)(2)=20$

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