# How can I sketch the graph of y=cos2x?

### 7 Answers

- rajLv 71 decade agoFavorite Answer
give x the values -pi/4,-pi/3,-pi/6,-pi/2,-pi,pi,6,pi/4,pi/3,pi/2,pi

find the values of cos 2x

i.e.cos(-pi/2),cos(-pi/6) etc

take it on the y axis and plot

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- LoreleiLv 44 years ago
If you really can't do it, sketch axes, then tap into your calculator the values. So pick x=0. Tap in cos0, cos(2*0). Draw the results on your sketch in different colours Then pick x=30. Tap in cos(30), cos(60) which is cos 2x. Draw the results on your sketch in different colours Then pick x=60. Tap in cos(60), cos(120). Draw the results on your sketch in different colours etc. You'll have your graph.

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- HelmutLv 71 decade ago
preferably with a pencil, so you can erase your mistakes.

The acceptable method of graphing any function is to set up a table of solution values, and plot the values on your graph.

You already know that -1 <= y <= 1 and the function repeats every pi radians or 180 degrees, right?

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- 1 decade ago
i used y=cos(2x) [i hope that's what you meant]

I get a sine wave with an amplitude of 1 and a wavelength of 3(about 3, a little more acutally)

If you can you might want to scale the y-axis by .25 and the x-axis by .5 or 1/3, that should make it easier to sketch.

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- alrivera_1Lv 41 decade ago
One way to plot this graph is to vary x from [0 to 360 degrees]. If you recall, the period of cosine(x) varies in this range. In this case, you have 2 times the angle x; when you complete this plot, you will find that you will have two complete cycles of cosine x in this period.

Please note that you can also work this problem using radians [0 to 2pi].

Good

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- Anonymous1 decade ago
Find the:

period

x and y intercepts

amplitude

From there it should be pretty straightforward. A graph in the interval [-2pi,2pi] should suffice.

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- Sherman81Lv 61 decade ago
for a graph, go to http://www.calculator.com/calcs/GCalc.html

type in cos(2x) or (cos(x))^2, depending if cos(x) is being squared or not

cos(2x) = cos(x)^2 - sin(x)^2 = 2cos(x)^2 - 1 = 1 - 2sin(x)^2

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