(a) Copy and complete the table of values for \(y = 2\cos x + 3\sin x\) for \(0^\circ \geq x \geq 360^\circ\)
| x |
\(0^\circ\) |
\(60^\circ\) |
\(120^\circ\) |
\(180^\circ\) |
\(240^\circ\) |
\(300^\circ\) |
\(360^\circ\) |
| y |
2.0 |
|
|
|
- 3.6 |
|
|
(b) Using a scale of 2cm to \(60^\circ\) on the x-axis and 2cm to 1 unit in the y-axis, draw the graph of \(y = 2\cos x + 3\sin x\) for \(0^\circ \geq 360^\circ\)
(c) Using the graph,
(i) Solve \(2\cos x + 3\sin x = -1\)
(ii) Find, correct to one decimal place, the value of y when \(x = 342^\circ\)
(a) Completing the table for \(y = 2\cos x + 3\sin x\). Using \(\sin60^\circ=\cos30^\circ=0.866\):
| x | 0° | 60° | 120° | 180° | 240° | 300° | 360° |
|---|
| y | 2.0 | 3.6 | 1.6 | -2.0 | -3.6 | -1.6 | 2.0 |
Sample working: at \(x=60^\circ,\ y=2(0.5)+3(0.866)=1.0+2.6=3.6\); at \(x=300^\circ,\ y=2(0.5)+3(-0.866)=1.0-2.6=-1.6\).
(b) Graph. Using 2 cm to 60° on the x-axis and 2 cm to 1 unit on the y-axis, plot the points and join with a smooth curve. It peaks near \(x=34^\circ\) (about 3.6) and dips near \(x=214^\circ\) (about -3.6).
(c)(i) Solve \(2\cos x + 3\sin x = -1\). Draw the line \(y=-1\). Since \(2\cos x+3\sin x=\sqrt{13}\,\sin(x+33.7^\circ)\), we need \(\sin(x+33.7^\circ)=-0.277\), giving
\[x \approx 162^\circ \quad\text{and}\quad x \approx 310^\circ.\]
(c)(ii) Value of y when \(x=342^\circ\). Read up from \(x=342^\circ\):
\[y = 2\cos342^\circ + 3\sin342^\circ = 2(0.951)+3(-0.309)=1.90-0.93 \approx 1.0.\]