Mark scheme
6(a) Sketch a relevant graph, e.g. y = cot 2 x 1 B1 2
cot(2x)
g( x ) =
Scales must be correct if seen. Do not need a full scale, but
tan ( 2∙x) do need to be able
to verify the key points mentioned below: 1
For y = cot 2 x, correct intercept on x-axis, asymptotes at x = 0, x = 12 π implied 2sin(2x)-1
(condone large gap between the curve and the asymptote on the RHS). Must
be continuous. π 3π π π O π π 3π π
For 2sin 2 x − 1, correct shape and position. No incorrect curvature.
4
Correct
2 4 4 2 4
maximum implied. Intercept at (0, -1). 1
Sketch a second relevant graph, e.g. y = 2sin 2 x − 1 and justify the given B1 Need
2
to see enough of both graphs to confirm there is
statement not a second intersection in the given interval. Need to
mark the intersection with a dot or a cross, or say that
the root lies at the point of intersection (or equivalent).
2
6(b) Calculate the values of a relevant expression or pair of expressions at M1 E.g. 0.9712 > 0.435 and 0.389 < 0.864
x = 0.4and x = 0.6 0.537 > 0 and − 0.475 < 0
Or using the iterative formula, 0.18 > 0, –0.17 < 0
Allow working on a smaller interval contained within the given interval Or using tan 2 x ( 2sin 2 x − 1) − 1 = 0 – 0.55 < 0,
and 1.22 > 0.
M0 if working in degrees.
Justify the given statement with correct calculated values A1 Values to 2 sf or better.
Accept values with statement f ( 0.4 ) × f ( 0.6 ) < 0.
2
6(c) 1 1 M1 M0 if working in degrees.
Use the iterative process xn+1 = tan −1 correctly at least once Need to get as far as a second iteration completed.
2 2sin 2 xn − 1
Obtain final answer 0.49 A1
Show sufficient iterations to 4 d.p. to justify 0.49 to 2 d.p. or show that there A1 E.g. 0.5,0.4858,0.4967,0.4883,0.4947,....
is a sign change in ( 0.485, 0.495 ) or 0.4, 0.5804, 0.4378, 0.5395, 0.4595, 0.5188, 0.4726,
–0.0157 < 0, 0.355 > 0 0.5075, 0.4804, 0.5009, 0.4851, 0.4972, 0.4879,
0.4950, 0.4895, 0.4937
or 0.6, 0.4291, 0.5483, 0.4544, 0.5235, 0.4695, 0.5101,
0.4786, 0.5025, 0.4840, 0.4981, 0.4872, 0.4955,
0.4891, 0.4940
The last 2 options are a lot of iterations. Allow the
marks if they start correctly and finish correctly.
Condone if there are some missing in the middle.
3