2x^3 + ax^2 + bx + 2 dibagi (x + 1) sisanya 6 dan dibagi oleh (x-2) sisanya 24. Nilai 2a - b =

jawab
f(x) = 2x³ + ax² + bx+ 2
x+1= 0 --> x = - 1 --> f(-1) =6
x - 2 = 0  --> x = 2  --> f(2) =24

f(-1) = 6
2(-1) + a(1) + b(-1) + 2 = 6
a - b  = 6

f(2) = 24
2(8) + a(4) +b(2) + 2 = 24
4a + 2b = 6
2a + b = 3

a  - b = 6
2a + b = 3 .....(+)
3a = 9
a= 3

b = a - 6
b = - 3

nilai 2a - b = 2(3) - (-3) = 6+3
2a - b = 9