### Question Description

x^2-20x

## Final Answer

A perfect square should be of the form:

(x + a)^2

So what must a be? Well, since we will multiply out brackets to make:

(x + a)^2

= x^2 + 2ax + a^2

Then we can see that 2a = -20 (from our original expression). So a = -10, therefore a^2 = 100.

So we need to add 100 to the expression :-)

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