Question

solve by multiplying x^2(2x+9)

Answer 1

Multiply (distribute) x^2 across the parentheses:

x^2(2x+9) = x^2·2x + x^2·9 = 2x^3 + 9x^2.

If you mean solve x^2(2x+9) = 0, then
x^2 = 0 ⇒ x = 0 (double root),
2x+9 = 0 ⇒ x = −9/2.