It is given that and .
- (i)
State the amplitude and period, in degrees, of
(a) ,
(b) . - (ii)
For the interval ,
solve the equation , - (iii)
sketch, on the same diagram, the graphs of and ,
- (iv)
find the set of values of for which .
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Worked solution
8(i)
1. Determine the amplitude and period of $y_1 = \sin x - 2$
For :
Amplitude
Period
2. Determine the amplitude and period of $y_2 = -3 \cos 2x$
For :
Amplitude
Period
(a) Amplitude = 1, Period =
(b) Amplitude = 3, Period =
8(ii)
1. Set up the equation and apply the double angle identity for cosine
2. Rearrange into a quadratic equation in terms of $\sin x$
3. Factorise and solve for $\sin x$
4. Find the values of $x$ in the given interval
For :
Basic angle
For :
Basic angle
8(iii)
1. Identify key features of $y_1 = \sin x - 2$
Amplitude = 1, Period = . The principal axis is . Maximum value = , minimum value = . Key points at are .
2. Identify key features of $y_2 = -3 \cos 2x$
Amplitude = 3, Period = . The principal axis is . Maximum value = , minimum value = . It is an inverted cosine graph. Key points for one cycle at are . The second cycle repeats these values up to .
3. Sketch both graphs on the same axes
Draw the axes for and . Plot the key points for and draw a smooth sine curve. Plot the key points for and draw two cycles of a smooth inverted cosine curve. Ensure the intersections align with the solutions from part (ii).
A sketch showing and on the same axes for .
8(iv)
1. Identify the intersection points from part (ii)
From part (ii), the solutions to are .
2. Use the graphs from part (iii) to determine where $y_2 > y_1$
The inequality is equivalent to .
From the sketch in part (iii), the curve lies above the curve between the first and second intersection points, and between the third and fourth intersection points.
Therefore, the required set of values is or .
or
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