5. All like terms can be combined. There will be one term remaining after they are.
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6. The appropriate factoring is x(x+1). This is not the same as x(2x+1).
In order to show equivalence, you need to show that the expressions produce the same result for as many different values of x as the degree of the expression plus 1. That is, you'd need to show equivalence for <em>3 different values of x</em>, as a minimum for this second-degree expression.
