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presume you mean find the values of x so that
$\displaystyle x^2(x+3)(x^2-1) = 0$
since this is already factored out. then setting any one of the factors to zero will work so..
if $\displaystyle x^2 = 0$ then $\displaystyle x = 0$
if $\displaystyle x+3=0$ then $\displaystyle x=-3$
if $\displaystyle x^2-1 = 0$ then$\displaystyle x= 1 $or $\displaystyle x= -1$