sine wave in excel

mufc802 · 22 Dec 2010 at 23:26

I'm learning about sine, cosine and tangent waves so thought I would make some in Excel, so I typed in the angles from 0 to 360 in 15 degrees intervals. To give the sin values I used the formula =SIN(ANGLE*PI()/180) which works. I'm not sure why on 360, and in the cycles after so 720 degrees it comes up with -2.4503E-16 for 360 and -4.90059E-16 for 720 instead of 0. Also for 180 it says 1.22515E-16 instead of 0?

mufc802 · 22 Dec 2010 at 23:32

flibbage0 said:
Format the cell so it only shows certain number of sig figs or decimal points?

Oops forgot to do that, it was set to general instead of number so no wonder it didn't make sense. Cheers.

mufc802 · 23 Dec 2010 at 11:36

ordinaryjoe said:
sorry if this is really stupidly obvious but you do know that the E means x10^ don't you? i.e. 2.5E-6 means 2.5x10^-6, so anything to the power of -16 is less than 1 millionth of a billionth

I guessed it meant something like that but not sure why it put that instead of 0.

Anyway, I'm puzzled about something else now..

The formula I used for the blue line is =2*SIN(ANGLE*PI()/180)+3*COS(ANGLE*PI()/180), so say the angle was 10, it would give an answer of 3.3017. What I want to find is the exact angle(s) for 3.5, so how do I reverse the formula to find them as there should be two where the line crosses the y axis. I could take a rough guess of 20 and 46 degrees looking at the graph but is there a way to get the exact answer using a formula?
Also, how do I find the max amplitude the line reaches by using some sort of formula instead of just looking at the graph?

mufc802 · 23 Dec 2010 at 12:01

physichull said:
You can cheat using Excel's Goalseek function for the 3.5 question, you can also use a couple of IF statments to find the max, alternatively use use Excel to use Conditional Formatting to highlight the max value.

If this is project work or whatever, then Goalseek is very much cheating!

No it's not a project it's just from a textbook I'm learning about waves. I've heard of Goalseek but can't remember how to use it, and how do the IF statements work to find the highest value on the graph and what's Conditional Formatting?

In the book it answers it by just saying just looking at the plotted graph and saying a rough guess for both answers. But how do you reverse the formula =2*SIN(10*PI()/180)+3*COS(10*PI()/180) which makes 3.3017, so reverse 3.5 to find the angles?