
4-9 Amplitude and period: y = a sin bx and y = a cos bx
Point 9 of 11 — Unit 4: Trigonometry — Directed Angles, Functions, Related Angles and GraphsQuestion bank: 0 questions (0 with pictures)
09 4-9 Amplitude and period: y = a sin bx and y = a cos bx
- Amplitude = |a|: the factor a stretches the curve vertically, so the range becomes [−|a|, |a|].
- Period = 360°/|b| in degrees, or 2π/|b| in radians: the factor b compresses or stretches the curve horizontally.
- Example: y = 3 sin 2x has amplitude 3 and period 180°; y = ½ cos 4x has amplitude ½ and period 90°.
- A negative a reflects the curve in the x-axis without changing amplitude or period; a negative b does not change the period either.
- Real-life use: tides, alternating current, and the height of a point on a wheel — read the maximum, minimum and one complete cycle from the graph.
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