What to do with trig functions?

• February 26th 2013, 06:25 AM
alexpasty2013
What to do with trig functions?
Hi could anyone direct me to a good text/vid or explain some things to me?

My course has gone to great lengths to explain all about the basic trig functions, sin being opp over hyp etc, but so far it has left out what you do with these functions, how to use them etc.

If I have opp = 30cm and hyp = 80cm and I divide them and I am left with 0.375 or whatever it is. Great. So sin = 0.375. Wonderful. Glad to know that. Now what!

The text does not explain what my 0.375 relates to, or what it is for? My angle is not 0.375 that does not sound right, the adj is not 0.375 either. What am I to do with my 0.375?
• February 26th 2013, 07:36 AM
HallsofIvy
Re: What to do with trig functions?
Quote:

Originally Posted by alexpasty2013
Hi could anyone direct me to a good text/vid or explain some things to me?

My course has gone to great lengths to explain all about the basic trig functions, sin being opp over hyp etc, but so far it has left out what you do with these functions, how to use them etc.

Did it not say sine of what was "opp over hyp"? Did it not say what "opp" meant?

Quote:

If I have opp = 30cm and hyp = 80cm and I divide them and I am left with 0.375 or whatever it is. Great. So sin = 0.375. Wonderful. Glad to know that. Now what!
The sine of an angle, in a right triangle, is the length of the leg opposite that angle, divided by the length of the hypotenuse. If the leg opposite angle A is 30 cm and the hypotenuse is 80 cm, then sin(A)= 30/80= 3/8= 0.375. If you want to find the measure of angle A you need to fine the inverse of the sine- your calculator has a "sin" key and either a " $sin^{-1}$" or an "inv" key. Ask your teacher about how to use your specific calculator if you need to.
In any case, the point is that "0.375" is NOT the angle itself but the sine of the angle. To find the angle itself, you need to find the "inverse sine". The calculator that comes with Windows has an INV key. Entering "0.375", then clicking on the "INV" key the "sin" key turns to " $sin^{-1}$" showing that it is now the invers function. Making sure the calculator is in "degree" mode, clicking on " $sin^{-1}$" gives 22.02431... telling us that the angle is about 22 degrees.