Changing the sign of \(a\) reflects the graph in its midline. The period is unchanged; assume \(b>0\).
\(\text{Sine/cosine amplitude}=|a|\qquad\text{Extremes}=c\pm|a|\)
| Curve | Reflection line | Amplitude | What changes |
|---|---|---|---|
| \(y=a\sin(bx),\ a<0\) | |||
| \(y=a\sin(bx)+c,\ a<0\) | |||
| \(y=a\cos(bx),\ a<0\) | |||
| \(y=a\cos(bx)+c,\ a<0\) | |||
| \(y=a\tan(bx),\ a<0\) |
For \(y=2-3\cos2x\), the midline is \(y=2\) and the amplitude is \(3\).
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