the equation x^2 - ax + b = 0 has two equal real roots,
2x^2 + ax - 12b = 0 is divisible by x + 3

我淨係識得
△ = 0
(-a)^2 - 4(1)(b) = 0
a^2 - 4b = 0 ...(1)
之後點做

搵a同b
求step

f4啲野唔記得哂 [/size=2]