數學功課唔識做,幫手 20點

求從3x^3+ 3x^2+ x- 1減去2x^3+ 3x2 -1的結果
3x^3+ 3x^2+ x- 1- (2x^3+ 3x2 -1)
3x^3+ 3x^2+ x- 1- 2x^3- 3x2 +1
x^3 + x


求3x+ 2乘以2x^ 3 +x^2 -1的結果
(3x+ 2)(2x^ 3 +x^2 -1)
6x^4 + 3x^3 – 3x + 4x^3 + 2x^2 – 2
6x^4 + 7x^3 – 3x + 2x^2 – 2
6x^4 + 7x^3 + 2x^2 – 3x – 2


求2x^3+ 6x^2+ x+ 5除以x+3的結果
(2x^3+ 6x^2+ x+ 5)/(x + 3)

2x^2 + 1
---------------------------
(x + 3)| 2x^3+ 6x^2+ x+ 5
2x^3+ 6x^2
--------------------------
x+ 5
x+ 3
--------
2


設f(x)=2x^3 +kx^2- 18x+ 8,其中k是常數。已知x- 2是f(x)的因式,求k的值
2x^3 +kx^2- 18x+ 8 = 0
2(2)^3 +k(2)^2 – 18(2)+ 8 = 0
16 + 4k – 36 +8 = 0
4k – 12 = 0
4k = 12
k = 12/4
k = 3