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f(x) = 2x^3 + x^2 - 5x + c, where c is a constant - Edexcel - A-Level Maths Pure - Question 3 - 2006 - Paper 2

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f(x)-=-2x^3-+-x^2---5x-+-c,-where-c-is-a-constant-Edexcel-A-Level Maths Pure-Question 3-2006-Paper 2.png

f(x) = 2x^3 + x^2 - 5x + c, where c is a constant. Given that f(1) = 0, (a) find the value of c. (b) factorise f(x) completely, (c) find the remainder when f(x) ... show full transcript

Worked Solution & Example Answer:f(x) = 2x^3 + x^2 - 5x + c, where c is a constant - Edexcel - A-Level Maths Pure - Question 3 - 2006 - Paper 2

Step 1

(a) find the value of c

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Answer

To find the value of c, we substitute x = 1 into the function:

f(1) = 2(1)^3 + (1)^2 - 5(1) + c = 0$$ This simplifies to:

2 + 1 - 5 + c = 0 \ -2 + c = 0 \ c = 2

Step 2

(b) factorise f(x) completely

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Answer

Given:

f(x)=2x3+x25x+2 f(x) = 2x^3 + x^2 - 5x + 2\

To factorise, we can first factor out common terms using synthetic division, dividing by (x - 1):

Upon performing synthetic division, we find:

f(x)=(x1)(2x2+3x2)  f(x) = (x - 1)(2x^2 + 3x - 2)\

Now we need to factor the quadratic expression:

2x2+3x2=(2x1)(x+2) 2x^2 + 3x - 2 = (2x - 1)(x + 2)\

Thus, the complete factorization is:

f(x)=(x1)(2x1)(x+2) f(x) = (x - 1)(2x - 1)(x + 2)\

Step 3

(c) find the remainder when f(x) is divided by (2x - 3)

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Answer

To find the remainder when dividing f(x) by (2x - 3), we can use the Remainder Theorem. We first need to find the value of x where 2x - 3 = 0:

2x=3x=322x = 3 \\ x = \frac{3}{2} \\

Now we substitute this value into f(x):

f(32)=2(32)3+(32)25(32)+2 f(\frac{3}{2}) = 2(\frac{3}{2})^3 + (\frac{3}{2})^2 - 5(\frac{3}{2}) + 2\

Calculating this:

f(32)=2278+94152+2=278+188608+168=98+68=158f(\frac{3}{2}) = 2\frac{27}{8} + \frac{9}{4} - \frac{15}{2} + 2 = \frac{27}{8} + \frac{18}{8} - \frac{60}{8} + \frac{16}{8} = \frac{-9}{8} + \frac{-6}{8} = -\frac{15}{8} \\

Thus, the remainder is:

158 -\frac{15}{8}

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