If has (x-2) as a factor and leaves a remainder 3 when divided by (x-3), find the values of a and b.
Let f(x) = (x3 + ax2 + bx + 6)
By using remainder theorem,
If we divide f(x) by (x – 3) then it will leave a remainder as f(3)
So,
f(3) = 32 + a × 32 + b × 3 + 6 = 3
27 + 9a + 3b + 6 = 3
9a + 3b + 33 = 3
9a + 3b = 3 – 33
9a + 3b = -30
3a + b = -10 (i)
It is also given that,
(x – 2) is a factor of f(x)
Therefore,
By using factor theorem, we get
(x – a) is the factor of f(x) if f(a) = 0and also f(2) = 0
Now,
f(2) = 23 + a × 22 + b × 2 + 6 = 0
8 + 4a + 2b + 6 = 0
4a + 2b = -14
2a + b = -7 (ii)
Now by subtracting (ii) from (i), we get
a = -3
Putting the value of a in (i), we get
3(-3) + b = -10
-9 + b = -10
b = -10 + 9
b = -1
Therefore,
b = -1 and a = -3