Question

Kari uses substitution to decide whether x2+x is equivalent to x(2x+1). She says the expressions are equivalent because they have the same value when x=0. Is Kari correct? Explain.

Answer 1

Kari is not correct. Plug in any value other than 0 for these and the answers you get will not be equal, simple as that. (ex. If x =3, x² + x = 12 and x(2x+1) = 21)

x = 0 would be a solution to the set of equations, but the question here is are all solutions valid, which is not so.