CAIE P3 2013 November — Question 2 4 marks

Exam BoardCAIE
ModuleP3 (Pure Mathematics 3)
Year2013
SessionNovember
Marks4
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicExponential Equations & Modelling
TypeQuadratic in exponential form
DifficultyStandard +0.3 This requires understanding of absolute value equations and exponential manipulation. Students must split into two cases (3^x ≥ 1 and 3^x < 1), solve each algebraically, then verify solutions. While it involves multiple steps and case analysis, the techniques are standard for P3 level and the algebraic manipulation is straightforward once cases are identified, making it slightly easier than average.
Spec1.02l Modulus function: notation, relations, equations and inequalities1.06g Equations with exponentials: solve a^x = b

Solve the equation \(2|3^x - 1| = 3^x\), giving your answers correct to 3 significant figures. [4]

AnswerMarks Guidance
EITHER: State or imply non-modular equation \(2^{'}(3^{x}-1)^{2}=(3^{x})^{2}\), or pair of equations \(2(3^{x}-1)=\pm 3^{x}\)M1
Obtain \(3^{x}=2\) and \(3^{x}=\frac{2}{3}\) (or \(3^{x+1}=2\))A1
OR: Obtain \(3^{x}=2\) by solving an equation or by inspectionB1
Obtain \(3^{x}=\frac{2}{3}\) (or \(3^{x+1}=2\)) by solving an equation or by inspectionB1
Use correct method for solving an equation of the form \(3^{x}=a\) (or \(3^{x+1}=a\)), where \(a>0\)M1
Obtain final answers \(0.631\) and \(-0.369\)A1 [4]
**EITHER:** State or imply non-modular equation $2^{'}(3^{x}-1)^{2}=(3^{x})^{2}$, or pair of equations $2(3^{x}-1)=\pm 3^{x}$ | M1 | 

Obtain $3^{x}=2$ and $3^{x}=\frac{2}{3}$ (or $3^{x+1}=2$) | A1 | 

**OR:** Obtain $3^{x}=2$ by solving an equation or by inspection | B1 | 

Obtain $3^{x}=\frac{2}{3}$ (or $3^{x+1}=2$) by solving an equation or by inspection | B1 | 

Use correct method for solving an equation of the form $3^{x}=a$ (or $3^{x+1}=a$), where $a>0$ | M1 | 

Obtain final answers $0.631$ and $-0.369$ | A1 | [4]
Solve the equation $2|3^x - 1| = 3^x$, giving your answers correct to 3 significant figures. [4]

\hfill \mbox{\textit{CAIE P3 2013 Q2 [4]}}