The sound produced by touching each button on a touch-tone phone is described by y = sin 2πlt + sin 2πht where l and h are the low and high frequencies (cycles per seconD. in the figure shown.
Use a calculator to find the graph of the sound emitted by touching the 4 key in a [0, 0.01, 0.001] by [-2, 2, 1] viewing rectangle.

Question

The sound produced by touching each button on a touch-tone phone is described by y = sin 2πlt + sin 2πht where l and h are the low and high frequencies (cycles per seconD. in the figure shown.
 Use a calculator to find the graph of the sound emitted by touching the 4 key in a [0, 0.01, 0.001] by [-2, 2, 1] viewing rectangle.

anonymous · Answer

attachment

anonymous · Answer

@sidsiddhartha ?

sidsiddhartha · Answer

so when you are touching key 4 then wats the frequency and what h?

sidsiddhartha · Answer

look frequency corresponding with key 4 is =770
and h=1209

sidsiddhartha · Answer

so put those in the equation
$$y=\sin2 \pi l t+\sin 2 \pi ht=\sin (2 \pi 770t)+\sin (2 \pi 1209 t)$$

sidsiddhartha · Answer

solve it using$$sinx+siny=2 \sin \frac{ x+y }{ 2 }.\cos \frac{ x-y }{ 2 }$$

sidsiddhartha · Answer

$$2 \sin \frac{ 1209+770 }{ 2 }\cos \frac{ 1209 -770}{ 2 }=2\sin(989.5)t.\cos(219.5)t$$

sidsiddhartha · Answer

http://www.wolframalpha.com/input/?i=plot+f%28t%29%3D2sin%28989.5+t%29*cos%28219.5+t%29 thats the graph

sidsiddhartha · Answer

look option C mathces

sidsiddhartha · Answer

i mean the last one in the picture

anonymous · Answer

its C or D?

anonymous · Answer

"I mean the last one in the picture" are you talking about D? Or?

sidsiddhartha · Answer

the picture u uploaded have only three pictures

anonymous · Answer

Yes cause the other one was wrong

sidsiddhartha · Answer

last one ,where D is written in the bottom

anonymous · Answer

what about it? It D the answer?