# trig exact values

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• Sep 23rd 2011, 11:08 PM
jmanna98
trig exact values
Please help me with finding trig exact values. I have always relied on my calculator to give me answers for these problems but now my prof. makes us use a calculator that cant convert decimals to fractions. I know how to do it with easy values when using the special triangles but what do I do when you have something like:

Find the exact value for cos(4/5)
• Sep 23rd 2011, 11:28 PM
CaptainBlack
Re: trig exact values
Quote:

Originally Posted by jmanna98
Please help me with finding trig exact values. I have always relied on my calculator to give me answers for these problems but now my prof. makes us use a calculator that cant convert decimals to fractions. I know how to do it with easy values when using the special triangles but what do I do when you have something like:

Find the exact value for cos(4/5)

Sorry but that makes no sense, your calculator can tell you what cos(0.8) is can't it?

It will also let you enter cos(4/5) directly

CB
• Sep 23rd 2011, 11:38 PM
jmanna98
Re: trig exact values
sorry the question is arccos(4/5), therefore cos(theta)=4/5. How would I find the angle?
• Sep 24th 2011, 12:50 AM
CaptainBlack
Re: trig exact values
Quote:

Originally Posted by jmanna98
sorry the question is arccos(4/5), therefore cos(theta)=4/5. How would I find the angle?

Think 3,4,5 triangle, and there is no "exact" value of arccos(4/5).

CB