✔ 最佳答案
∵ (x+2)(x-1)(2x+c) = (x^2 +x -2)(2x+c) = 2x^3 + 2x^2 -4x + cx^2 + cx -2c
= 2x^3 +(2+c) x^2 +( c-4) x -2c
i.e. 2x³-ax+b = 2x^3 +(2+c)x^2+( c-4)x -2c
比對系數,
2+ c = 0 => c = -2,
c -4 = -a => -2-4 = -a => a = 6
b = -2c => b =(-2) (-2) = 4
∴ a+b+c= 6+4-2 = 8
_________________________________________________________
同學:
* 此款數題,多考慮以 「比對系數」作為運算策略!
* 可代入答案: a = 6,b = 4,c = -2 於題目的公式中,作為驗証