# Having trouble reducing a fraction using trig identities

• May 11th 2012, 06:10 PM
KarlKarlJohn
Having trouble reducing a fraction using trig identities
I am having trouble with a trig identity problem. The book I am working out of provides step by step solutions and we are in agreement up to this point

[1 + 2Cos(x) - Sin2(x) + Cos2(x)] / 2Sin(x)Cos(x)

Here is where I went from there...

I turned the Sin2(x) + Cos2(x) into 1 in order to get

2Cos(x) / 2Sin(x)Cos(x)

I then cancelled to get a final result of

1/Sin(x) or CSC(x)

Here is what the book did...

the book substituted 1-Cos2(x) in for Sin2(x) in order to get

[2Cos(x) + 2Cos2(x)] / 2Sin(x)Cos(x)

They then factored a 2Cos(x) out of the numerator and cancelled to get a final result of

[1 + Cos(x)] / Sin(x)

I understand why the book's method makes sense and works. What I can't figure out is why my way doesn't. If for example I substitute 17 in for x my method yields a result of 3.42 while their method results in 6.69. I'd appreciate any help or insight into what mistakes I'm making. If by some random chance someone reading this has the same book, I'm using Trigonometry Workbook for Dummies and working on problem 18 in chapter 11
• May 11th 2012, 06:25 PM
emakarov
Re: Having trouble reducing a fraction using trig identities
Quote:

Originally Posted by KarlKarlJohn
[1 + 2Cos(x) - Sin2(x) + Cos2(x)] / 2Sin(x)Cos(x)

Here is where I went from there...

I turned the Sin2(x) + Cos2(x) into 1 in order to get

2Cos(x) / 2Sin(x)Cos(x)

You have Cos2(x) - Sin2(x), not Cos2(x) + Sin2(x).
• May 11th 2012, 06:40 PM
KarlKarlJohn
Re: Having trouble reducing a fraction using trig identities
Quote:

Originally Posted by emakarov
You have Cos2(x) - Sin2(x), not Cos2(x) + Sin2(x).

Thanks, for the quick response, makes complete sense. I think I just got so eager to use an identity when I saw Sin2(x) + Cos2(x) that I forgot how to add (Rofl). Thanks again for the help!