Edexcel C3 2014 June — Question 5 8 marks

Exam BoardEdexcel
ModuleC3 (Core Mathematics 3)
Year2014
SessionJune
Marks8
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicModulus function
TypeSketch y=|linear| and y=linear, solve inequality: numeric coefficients
DifficultyModerate -0.3 This is a standard C3 modulus question requiring a routine sketch and solving two linear modulus inequalities using the V-shaped graph or algebraic cases. Part (a) is straightforward, parts (b) and (c) require splitting into cases or graphical interpretation but follow textbook methods with no novel insight required. Slightly easier than average due to the linear nature and standard technique application.
Spec1.02g Inequalities: linear and quadratic in single variable1.02h Express solutions: using 'and', 'or', set and interval notation1.02l Modulus function: notation, relations, equations and inequalities

5. (a) Sketch the graph with equation $$y = | 4 x - 3 |$$ stating the coordinates of any points where the graph cuts or meets the axes. Find the complete set of values of \(x\) for which
(b) $$| 4 x - 3 | > 2 - 2 x$$ (c) $$| 4 x - 3 | > \frac { 3 } { 2 } - 2 x$$

Question 5(a):
AnswerMarks Guidance
Answer/WorkingMark Guidance
V shaped graphB1
Touches \(x\)-axis at \(\frac{3}{4}\) and cuts \(y\)-axis at \(3\)B1
Question 5(b):
AnswerMarks Guidance
Answer/WorkingMark Guidance
Solves \(4x-3=2-2x\) or \(3-4x=2-2x\) to give either value of \(x\)M1
Both \(x=\frac{5}{6}\) and \(x=\frac{1}{2}\), or \(x>\frac{5}{6}\) or \(x<\frac{1}{2}\)A1
\(x<\frac{1}{2}\) or \(x>\frac{5}{6}\)dM1 A1
Question 5(c):
AnswerMarks Guidance
Answer/WorkingMark Guidance
Draws graph or solves \(4x-3 =1\frac{1}{2}-2x\) to give one solution \(x=\frac{3}{4}\)
All values of \(x\) except \(x=\frac{3}{4}\), i.e. \(x\neq\frac{3}{4}\), or \(x<\frac{3}{4}\), \(x>\frac{3}{4}\)A1
Question 5 (Absolute Value/Modulus):
Part (a):
AnswerMarks Guidance
AnswerMark Guidance
V-shaped graphB1 Must be V-shape, not a curve. Accept V shape with dotted extension of \(y = 4x-3\) under x-axis
Meets x-axis at \(x = \frac{3}{4}\), crosses y-axis at \(y = 3\)B1 \(A = \left(\frac{3}{4}, 0\right)\) and \(B = (0,3)\). Condone \(\left(0, \frac{3}{4}\right)\) and \((3,0)\) marked on correct axis
Part (b):
AnswerMarks Guidance
AnswerMark Guidance
Attempts to solve \(4x-3 \ldots 2-2x\), finding at least one solution
Both critical values \(x = \frac{5}{6}\) and \(x = \frac{1}{2}\)A1 Accept \(x = 0.83\) and \(x = 0.5\). Or one inequality \(x > \frac{5}{6}\) or \(x < \frac{1}{2}\)
Selects outside regiondM1 Dependent on previous M. E.g. if \(x = 0.83\) and \(x = -2.5\) found, correct application gives \(x < -2.5, x > 0.83\)
\(x < \frac{1}{2}\) or \(x > \frac{5}{6}\)A1 Accept \(x < 0.5, x > 0.83\)
Part (c):
AnswerMarks Guidance
AnswerMark Guidance
Sketch both lines showing single intersection at \(x = \frac{3}{4}\), or solves \(4x-3 = 1\frac{1}{2} - 2x\) using both \(4x-3 = 1\frac{1}{2}-2x\) and \(-4x+3 = 1\frac{1}{2}-2x\) giving one solution
Solution set is all values apart from \(x = \frac{3}{4}\)A1 Accept: all values of \(x\) except \(x = \frac{3}{4}\), or \(x \in \mathbb{R},\ x \neq \frac{3}{4}\), or \(x < \frac{3}{4},\ x > \frac{3}{4}\)
# Question 5(a):

| Answer/Working | Mark | Guidance |
|---|---|---|
| V shaped graph | B1 | |
| Touches $x$-axis at $\frac{3}{4}$ and cuts $y$-axis at $3$ | B1 | |

# Question 5(b):

| Answer/Working | Mark | Guidance |
|---|---|---|
| Solves $4x-3=2-2x$ or $3-4x=2-2x$ to give either value of $x$ | M1 | |
| Both $x=\frac{5}{6}$ and $x=\frac{1}{2}$, or $x>\frac{5}{6}$ or $x<\frac{1}{2}$ | A1 | |
| $x<\frac{1}{2}$ or $x>\frac{5}{6}$ | dM1 A1 | |

# Question 5(c):

| Answer/Working | Mark | Guidance |
|---|---|---|
| Draws graph or solves $|4x-3|=1\frac{1}{2}-2x$ to give one solution $x=\frac{3}{4}$ | M1 | |
| All values of $x$ except $x=\frac{3}{4}$, i.e. $x\neq\frac{3}{4}$, or $x<\frac{3}{4}$, $x>\frac{3}{4}$ | A1 | |

# Question 5 (Absolute Value/Modulus):

## Part (a):
| Answer | Mark | Guidance |
|--------|------|----------|
| V-shaped graph | B1 | Must be V-shape, not a curve. Accept V shape with dotted extension of $y = 4x-3$ under x-axis |
| Meets x-axis at $x = \frac{3}{4}$, crosses y-axis at $y = 3$ | B1 | $A = \left(\frac{3}{4}, 0\right)$ and $B = (0,3)$. Condone $\left(0, \frac{3}{4}\right)$ and $(3,0)$ marked on correct axis |

## Part (b):
| Answer | Mark | Guidance |
|--------|------|----------|
| Attempts to solve $|4x-3| \ldots 2-2x$, finding at least one solution | M1 | Accept $\pm4x \pm 3 = 2-2x \Rightarrow x = ..$ or $\pm4x \pm 3 > 2-2x \Rightarrow x > ..$ or $x < ..$ |
| Both critical values $x = \frac{5}{6}$ and $x = \frac{1}{2}$ | A1 | Accept $x = 0.83$ and $x = 0.5$. Or one inequality $x > \frac{5}{6}$ or $x < \frac{1}{2}$ |
| Selects outside region | dM1 | Dependent on previous M. E.g. if $x = 0.83$ and $x = -2.5$ found, correct application gives $x < -2.5, x > 0.83$ |
| $x < \frac{1}{2}$ or $x > \frac{5}{6}$ | A1 | Accept $x < 0.5, x > 0.83$ |

## Part (c):
| Answer | Mark | Guidance |
|--------|------|----------|
| Sketch both lines showing single intersection at $x = \frac{3}{4}$, **or** solves $|4x-3| = 1\frac{1}{2} - 2x$ using both $4x-3 = 1\frac{1}{2}-2x$ and $-4x+3 = 1\frac{1}{2}-2x$ giving one solution | M1 | If two values obtained it is M0A0 |
| Solution set is all values apart from $x = \frac{3}{4}$ | A1 | Accept: all values of $x$ except $x = \frac{3}{4}$, or $x \in \mathbb{R},\ x \neq \frac{3}{4}$, or $x < \frac{3}{4},\ x > \frac{3}{4}$ |

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5. (a) Sketch the graph with equation

$$y = | 4 x - 3 |$$

stating the coordinates of any points where the graph cuts or meets the axes.

Find the complete set of values of $x$ for which\\
(b)

$$| 4 x - 3 | > 2 - 2 x$$

(c)

$$| 4 x - 3 | > \frac { 3 } { 2 } - 2 x$$

\hfill \mbox{\textit{Edexcel C3 2014 Q5 [8]}}