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1. (a) Find the remainder when $x^3 - 2x^2 - 4x + 8$ is divided by (i) $x - 3$, (ii) $x + 2$ - Edexcel - A-Level Maths Pure - Question 4 - 2008 - Paper 2

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1.-(a)-Find-the-remainder-when--$x^3---2x^2---4x-+-8$--is-divided-by--(i)-$x---3$,--(ii)-$x-+-2$-Edexcel-A-Level Maths Pure-Question 4-2008-Paper 2.png

1. (a) Find the remainder when $x^3 - 2x^2 - 4x + 8$ is divided by (i) $x - 3$, (ii) $x + 2$. (b) Hence, or otherwise, find all the solutions to the equation ... show full transcript

Worked Solution & Example Answer:1. (a) Find the remainder when $x^3 - 2x^2 - 4x + 8$ is divided by (i) $x - 3$, (ii) $x + 2$ - Edexcel - A-Level Maths Pure - Question 4 - 2008 - Paper 2

Step 1

(i) $x - 3$

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Answer

To find the remainder when dividing by x3x - 3, we use the Remainder Theorem, which states that the remainder of the division of a polynomial f(x)f(x) by xcx - c is f(c)f(c). Here, we find:

f(3)=332(3)24(3)+8f(3) = 3^3 - 2(3)^2 - 4(3) + 8
=271812+8= 27 - 18 - 12 + 8
=5= 5
Thus, the remainder when x32x24x+8x^3 - 2x^2 - 4x + 8 is divided by x3x - 3 is 5.

Step 2

(ii) $x + 2$

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Answer

Similarly, for x+2x + 2, we evaluate:

f(2)=(2)32(2)24(2)+8f(-2) = (-2)^3 - 2(-2)^2 - 4(-2) + 8
=88+8+8= -8 - 8 + 8 + 8
=0= 0
Therefore, the remainder when x32x24x+8x^3 - 2x^2 - 4x + 8 is divided by x+2x + 2 is 0.

Step 3

b) Hence, or otherwise, find all the solutions to the equation $x^3 - 2x^2 - 4x + 8 = 0$.

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Answer

Since we found that x+2x + 2 is a factor (with a remainder of 0), we can factor the polynomial as:

x32x24x+8=(x+2)(Ax2+Bx+C)x^3 - 2x^2 - 4x + 8 = (x + 2)(Ax^2 + Bx + C)

To find AA, BB, and CC, we can perform polynomial long division, or by comparing coefficients. After simplification, we get:

(x+2)(x24)=(x+2)(x2)(x+2)(x + 2)(x^2 - 4) = (x + 2)(x - 2)(x + 2)
Thus, we set:

x+2=0x + 2 = 0
x2=0x - 2 = 0

Finding solutions: x=2,extmultiplicity2,x=2x = -2, ext{ multiplicity 2}, x = 2 Therefore, the solutions to the equation x32x24x+8=0x^3 - 2x^2 - 4x + 8 = 0 are x=2x = -2 (double root) and x=2x = 2.

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