The variables x and y are related in such a way that when lg y is plotted against lg x a straight line graph is obtained as shown in the diagram. The line passes through the points (2, 4) and (8, 7).
- (i)Express y in terms of x, giving your answer in the form y = axᵇ, where a and b are constants.[5]
- (ii)the gradient,[1]
- (iii)the intercept on the vertical axis?[1]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2012). The mark or mark type is shown in brackets.
- [B1] Finding gradient
- [M1] Finding y intercept
- [M1] lgy = c + mlgx is sufficient
- [A1] a = 1000 or 10³
- [A1] y = 1000x⁰.⁵ or 1000√x
- [B1] m = 1
- [B1] c = 6
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