MRSM Trial 2025 Add Maths Paper 2, Question 11Linear Law
Solved on video in English · Form 4, Linear Law · 7:02 video
The question
Table 1.1 shows the values of two variables x and y obtained from an experiment. The variables are related by y = px + r/(px), where p and r are constants. Table 1.1: x = 1, 2, 3, 4, 5, 6 ; y = 5.9, 4.2, 4.3, 4.6, 5.1, 5.9.
(a)(i) Based on Table 1.1, complete Table 1.2 (the xy row, given the x² row = 1, 4, 9, 16, 25, 36).
Table 1.1 gives x = 1, 2, 3, 4, 5, 6 and y = 5.9, 4.2, 4.3, 4.6, 5.1, 5.9 for y = px + r/(px).
(a)(ii) Plot xy against x², using a scale of 2 cm to 5 units on both axes. Hence, draw the line of best fit.
Using the straight-line graph of xy against x² (from y = px + r/(px), where xy = p·x² + r/p):
(b)(i) Using the graph in (a)(ii), find p.
Using the straight-line graph of xy against x² (xy = p·x² + r/p, with p = 0.8429):
(b)(ii) Using the graph in (a)(ii), find r.
The variables are related by y = px + r/(px), with p = 0.8429 and r = 4.214.
(c) Hence, find the values of the gradient and y-intercept for another possible linear form for y = px + r/(px).
7:02Part (a)(i)
Step 1
Compute xy = x·y for each column: x=1 → 5.9; x=2 → 8.4; x=3 → 12.9; x=4 → 18.4; x=5 → 25.5; x=6 → 35.4 (paired with x² = 1, 4, 9, 16, 25, 36).
Why this step
This row must be x × y because the straight line form we plot is xy against x². Watch for slips like x²·y or x + y.
Final answer
xy = 5.9, 8.4, 12.9, 18.4, 25.5, 35.4
Where students lose marks
Watch out: the row is x × y, not x²·y or x + y.
Part (a)(ii)
3 more steps, each with the reason for it, in the full solution
Final answer
Graph plotted (see video)
Where students lose marks
Watch out: plot xy against x², not x, use a uniform scale, and draw the line so the points balance on both sides.
Part (b)(i)
2 more steps, each with the reason for it, in the full solution
Final answer
p = 0.8429
Where students lose marks
Watch out: p is the gradient of the line, not the intercept.
Part (b)(ii)
2 more steps, each with the reason for it, in the full solution
Final answer
r = 4.214
Where students lose marks
Watch out: the y-intercept is r/p, not r. Multiply it by p to get r.
Part (c)
2 more steps, each with the reason for it, in the full solution
Final answer
gradient = 5, y-intercept = 0.8429
Where students lose marks
Watch out: for y/x against 1/x², the gradient is r/p and the intercept is p, the reverse of xy against x².
Watch every step of this question solved on video (7:02), with the reason behind each step and a box that checks your own answer.
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