Iterations: WJEC GCSE Higher November 2016 Unit 2 Q4

Higher November 2016 Unit 2 Q4

WJECHigherCurrent spec4 marksIterations

4. A solution to the equation

\[2x^3 - 3x - 17 = 0\]

lies between 2 and 3.

Use the method of trial and improvement to find this solution correct to 1 decimal place.
You must show all your working. [4]

Mark scheme

Scheme	Marks	Comments
One correct evaluation \(2 \leqslant x \leqslant 3\)	B1
2 correct evaluations \(2{\cdot}15 \leqslant x \leqslant 2{\cdot}35\), ( one value < 0, one value > 0.)	B1
2 correct evaluations \(2{\cdot}25 \leqslant x \leqslant 2{\cdot}35\), ( one value < 0, one value > 0.)	M1
\(x = 2{\cdot}3\)	A1

Correct evaluation regarded as enough to identify if negative or positive. If evaluations not seen accept ‘too high’ or ‘too low’.