2. Consider the real polynomial: q (x) = x3 β 2x2 + ax β b + 1 Determine the values of a and b so that q (x) + 1 is divisible by (x + 2) and q (x) has a root at x = 1.
Accepted Solution
A:
To determine the values of a and b, we'll use the given conditions:
q(x) + 1 is divisible by (x + 2).
q(x) has a root at x = 1.
Let's address these conditions one by one.
Condition 1: q(x) + 1 is divisible by (x + 2)
For a polynomial to be divisible by (x + 2), it must have (x + 2) as a factor. Therefore, we can write q(x) + 1 as (x + 2) multiplied by some other polynomial, say p(x):
q(x) + 1 = (x + 2) * p(x)
Expanding q(x) and simplifying:
x^3 - 2x^2 + ax - b + 1 = xp(x) + 2p(x)
Comparing the coefficients on both sides, we have:
x^3 = xp(x) (coefficients of x^3 on both sides)
-2x^2 + ax - b + 1 = 2p(x) (coefficients of x^2, x, and constant term on both sides)
From equation 1), we see that p(x) must be x^2 for x^3 to be equal to xp(x).
Substituting p(x) = x^2 into equation 2):
-2x^2 + ax - b + 1 = 2x^2
Now, let's simplify this equation further.
3x^2 + ax - (b + 1) = 0
Now, we have a quadratic equation. To satisfy condition 1, the discriminant of this quadratic equation must be zero, since (x + 2) should be a factor of q(x) + 1.
The discriminant is given by:
D = a^2 - 4ac
Substituting the coefficients:
D = a^2 - 4 * 3 * (-(b + 1))
D = a^2 + 12b + 12
For the discriminant to be zero:
a^2 + 12b + 12 = 0 ----(Equation 3)
Now, let's move on to condition 2.
Condition 2: q(x) has a root at x = 1
For q(x) to have a root at x = 1, we substitute x = 1 into the polynomial q(x) and equate it to zero:
q(1) = 1^3 - 2(1)^2 + a(1) - b + 1 = 0
Simplifying this equation:
1 - 2 + a - b + 1 = 0
a - b = 0 ----(Equation 4)
Now, we have two equations (Equation 3 and Equation 4) involving the variables a and b. We can solve these simultaneous equations to find the values of a and b.
From Equation 4, we have:
a = b
Substituting this value of a into Equation 3:
b^2 + 12b + 12 = 0
This is a quadratic equation in b. Solving it using any quadratic equation solver, we find the values of b:
b = -6 Β± β(6)
Since a = b, the corresponding values of a are:
a = -6 Β± β(6)
Therefore, the values of a and b that satisfy the given conditions are:
a = -6 + β(6)
b = -6 + β(6)
or
a = -6 - β(6)
b = -6 - β(6)