-x^ three *exp(-x) + three *x^ two *exp(-x) = zero
minus x cubed multiply by exponent of ( minus x) plus 3 multiply by x squared multiply by exponent of ( minus x) equally 0
minus x to the power of three multiply by exponent of ( minus x) plus three multiply by x to the power of two multiply by exponent of ( minus x) equally zero
-x3*exp(-x) + 3*x2*exp(-x) = 0
-x3*exp-x + 3*x2*exp-x = 0
-x³*exp(-x) + 3*x²*exp(-x) = 0
-x to the power of 3*exp(-x) + 3*x to the power of 2*exp(-x) = 0