CAIE P3 2022 June — Question 3 5 marks

Exam BoardCAIE
ModuleP3 (Pure Mathematics 3)
Year2022
SessionJune
Marks5
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicFactor & Remainder Theorem
TypeSingle polynomial, two remainder/factor conditions
DifficultyModerate -0.3 This is a straightforward application of the factor and remainder theorems requiring two substitutions to create simultaneous equations. The arithmetic involves fractions but the method is standard textbook procedure with no conceptual challenges or novel problem-solving required.
Spec1.02j Manipulate polynomials: expanding, factorising, division, factor theorem

3 The polynomial \(a x ^ { 3 } + x ^ { 2 } + b x + 3\) is denoted by \(\mathrm { p } ( x )\). It is given that \(\mathrm { p } ( x )\) is divisible by ( \(2 x - 1\) ) and that when \(\mathrm { p } ( x )\) is divided by \(( x + 2 )\) the remainder is 5 . Find the values of \(a\) and \(b\).

Question 3:
AnswerMarks Guidance
Substitute \(x = \frac{1}{2}\), equate result to zeroM1 Or divide by \(2x-1\) and equate constant remainder to zero
Obtain a correct simplified equationA1 e.g. \(\frac{1}{8}a + \frac{1}{4} + \frac{1}{2}b + 3 = 0\) or \(a + 4b = -26\)
Substitute \(x = -2\), equate result to 5M1 Or divide by \(x+2\) and equate constant remainder to 5
Obtain a correct simplified equationA1 e.g. \(-8a + 4 - 2b + 3 = 5\) or \(8a + 2b = 2\)
Obtain \(a = 2\) and \(b = -7\)A1 WWW
Total: 5 marks
## Question 3:

| Substitute $x = \frac{1}{2}$, equate result to zero | M1 | Or divide by $2x-1$ and equate constant remainder to zero |
|---|---|---|
| Obtain a correct simplified equation | A1 | e.g. $\frac{1}{8}a + \frac{1}{4} + \frac{1}{2}b + 3 = 0$ or $a + 4b = -26$ |
| Substitute $x = -2$, equate result to 5 | M1 | Or divide by $x+2$ and equate constant remainder to 5 |
| Obtain a correct simplified equation | A1 | e.g. $-8a + 4 - 2b + 3 = 5$ or $8a + 2b = 2$ |
| Obtain $a = 2$ and $b = -7$ | A1 | WWW |

**Total: 5 marks**

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3 The polynomial $a x ^ { 3 } + x ^ { 2 } + b x + 3$ is denoted by $\mathrm { p } ( x )$. It is given that $\mathrm { p } ( x )$ is divisible by ( $2 x - 1$ ) and that when $\mathrm { p } ( x )$ is divided by $( x + 2 )$ the remainder is 5 .

Find the values of $a$ and $b$.\\

\hfill \mbox{\textit{CAIE P3 2022 Q3 [5]}}