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Exercise 4.1 · Q2

Q.Find the period and amplitude of

(i) y=sin⁡7xy = \sin 7x
(ii) y=−sin⁡(13x)y = -\sin\left(\dfrac13 x\right)
(iii) y=4sin⁡(−2x)y = 4\sin(-2x).
Puducherry TnboardTextbookSubjectiveImportance★★★★★
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✓ Free question

Every part is a sinusoid y=Asin⁡(bx)y=A\sin(bx); we read off ∣A∣|A| as the amplitude and 2π∣b∣\dfrac{2\pi}{|b|} as the period directly from the coefficient of xx and the overall scale factor.

Step 1. (i) Identify AA and bb for y=sin⁡7xy=\sin 7x. Here A=1, b=7A=1,\ b=7. Amplitude =∣A∣=1=|A|=1; period =2π7=\dfrac{2\pi}{7}.

Step 2. (ii) Identify AA and bb for y=−sin⁡(13x)y=-\sin\left(\dfrac13x\right). Here A=−1, b=13A=-1,\ b=\dfrac13. Amplitude =∣−1∣=1=|-1|=1; period =2π1/3=6π=\dfrac{2\pi}{1/3}=6\pi.

Step 3. (iii) Rewrite y=4sin⁡(−2x)y=4\sin(-2x). Since sin⁡(−θ)=−sin⁡θ\sin(-\theta)=-\sin\theta, y=4sin⁡(−2x)=−4sin⁡(2x)y=4\sin(-2x)=-4\sin(2x), so A=−4, b=2A=-4,\ b=2. Amplitude =∣−4∣=4=|-4|=4; period =2π2=π=\dfrac{2\pi}{2}=\pi.

✓Final answer

(i) period 2π7\dfrac{2\pi}7, amplitude 11. (ii) period 6π6\pi, amplitude 11. (iii) period π\pi, amplitude 44.

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