Question

What must be added to f(x) = 4x4 + 2x3 -2x2 +x - 1, so that the resulting  polynomial  is divisible  by  g(x) = x2 +2x -3?​

Answer 1

Answer:

p(x) = -4*x^4  - 2*x^3 + 3*x^2 + 1*x - 2

Step-by-step explanation:

We want to find a polynomial p(x), such that if we add that polynomial to:

f(x) = 4*x^4 + 2*x^3 - 2*x^2 + x - 1

we get:

g(x) = x^2 + 2*x - 3

This is:

f(x) + p(x) = g(x)

Notice that f(x) is a polynomial of degree 4 and g(x) is a polinomial of degree 2, so p(x) must be also a polynomial of degree 4.

p(x) = a*x^4 + b*x^3 + c*x^2 + d*x + e

Then we get:

(4*x^4 + 2*x^3 - 2*x^2 + x - 1) + (a*x^4 + b*x^3 + c*x^2 + d*x + e) = x^2 + 2*x - 3

We can simplify the left side to:

(4 + a)*x^4 + (2 + b)*x^3 + (-2 + c)*x^2 + (1 + d)*x + (-1 + e) =  x^2 + 2*x - 3

Because in the right side we do not have terms with exponent 4 and 3, we must have that:

4 + a = 0

2 + b = 0

and for the other exponents of x we just match the exponent in the left side with the correspondent one in the right side:

(-2 + c) = 1

(1 + d) = 2

(-1 + e) = -3

Solving the 5 equations we get:

a = -4

b = -2

c = 1 + 2 = 3

d = 2 - 1 = 1

e = -3 + 1 = -2

Then the equation for p(x) is:

p(x) = -4*x^4  - 2*x^3 + 3*x^2 + 1*x - 2