Verified answer

(-3)^2+(-3)a-15=0

9-3a-15=0

a= - 2

x^2-2x-15=0

(x-5)(x+3)=0

Ans: a = -2, 另一根為 5

因為-3是方程式的根,所以帶入方程式等號會成立

x^2+(-3)a-15=0,a=-2

所以方程式為x^2-2x-15=0

x=-3or5

所以另一根是5

Sub. -3 into the equation: (-3)^2 +a(-3) - 15 = 0 9 - 3a - 15 = 0 a = -2. So the equation is x^2 - 2x - 15 = 0. (x +3)(x - 5) = 0 the other root is 5

put x=-3 in the x^2+ax-15=0

(-3)^2-3a-15=0

a=-2

x^2-2x-15=0

x=5 or x=-3