Trig Question

[eliot15]

Is there a way to solve for x below:

cos x = .9315

other than just starting to try:

cos 21 = .9336,
cos 21.5 = .9304,
etc. etc.
until I finally hit on,
oh, cos of 21.33 = .9315

I have a TI-30XA calculator.

Thanks

[eliot15]

Are we talking tables???

I found this Carr Lane "Trigonometry Tables and Handy References for Engineers".

I found the 21 degree page, looked under the 'M' column for 33, looked across to the Cosine column and found the value .93010, not .9315.

Does that 'M' by any chance stand for 'minutes'. Can I work in decimal degrees?? Whats the difference?? Is conversion between minutes and seconds, and decimal degrees, possible????

By the way, is it Hours, Minutes, Seconds? Not sure about the Hours part....

[eliot15]

I'm a little closer.

Figured out its Degrees, Minutes, Seconds...and this UTube video showed me how to convert from minutes to decimal degrees (minutes/60).

So in my table, I find the value 0.93148 under Cosine in the 20M row. Thats 20 minutes, I'm thinking. So if I divide 20/60, I get .33333333333, which gives me my 21.33.

Ok, ok...

So I'm thinking thats how its done...you just flip through your tables looking for the value closest to your Cosine value, which in my table gives me degrees and minutes, and the convert to decimal degrees if you want.

That about it???

[christinandavid]

Arccos or 'Inverse' Cos or cos ^-1 is what you are after. Usually obtained by hitting shift/2nd function button before hitting Cos button.

DP

[eliot15]

Thanks. Worked great!