Question

3. Find the value of p in each of the following when f(x) is divided by d(x), with the help of remainder theorem:

Answer 1

The remainder theorem says that dividing a polynomial f(x) by a 1st-degree polynomial g(x) = x - c leaves a remainder of exactly f(c).

(a) With f(x) = px ³ + 4x - 10 and d(x) = x + 3, we have a remainder of 5, so

f (-3) = p (-3)³ + 4(-3) - 10 = 5

Solve for p :

-27p - 12 - 10 = 5

-27p = 27

p = -1

(b) With f(x) = x + 3x ² - px + 4 and d(x) = x - 2, we have remainder 8, so

f (2) = 2 + 3(2)² - 2p + 4 = 8

-2p = -10

p = 5

(you should make sure that f(x) was written correctly, it's a bit odd that there are two x terms)

(c) f(x) = 2x ³ - 4x ² + 6x - p, d(x) = x - 2, R = f (2) = 18

f (2) = 2(2)³ - 4(2)² + 6(2) - p = 18

12 - p = 18

p = -6

The others are done in the same fashion. You would find

(d) p = 14

(e) p = -4359

(f) p = 10

(g) p = -13/2 … … assuming you meant f(x) = x ⁴ + x ³ + px ² + x + 20