X- 3X+a=X^+x+18则a+b等于

To solve this equation, we need to expand the left side and then set it equal to the right side:

(X-3)(X+a) = X^2 + (a-3)X - 3a

Setting it equal to the right side:

X^2 + (a-3)X - 3a = X^2 + X + 18

By comparing the coefficients of corresponding powers of X, we get:

a - 3 = 1 (coefficient of X) -3a = 18 (constant term)

Solving the second equation for a:

-3a = 18 a = -6

Substituting the value of a into the first equation:

a - 3 = 1 -6 - 3 = 1 -9 = 1

Since this equation is not true, it means there is no value of a that satisfies the equation. Therefore, we cannot determine the value of a+b