Maths help (trigonometry) +REP

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10-10-2012, 05:44 PM
Matthew

Maths help (trigonometry) +REP

Hiya

I'm completely stumped with this one. Its about proving identities.

You need to prove the following identity (take = to be the 'is identical to' sign):

1/sinx - sinx = cosx/tanx

I think I'm on the right lines, but get stuck at a point?

I do the following (hopefully this makes sense as its hard to read when fractions are written out on a computer as x/y IMO :()

1/sinx - sinx = cosx/tanx

1/sinx - sinx = 1-sin²x/sinx

1-sin²x/sinx = cos²x/sinx

where do I go from here? I'm now up to cos²x/sinx = cosx/tanx

Thanks if anyone can help lol, I bet its easy and I'm just being an idiot though :(
10-10-2012, 05:49 PM
Chippiewill

you're basically there, cos^2(x)/sinx = (cosx/sinx) * cosx = 1/tanx * cosx = cosx/tanx

You probably didn't notice that

cosx / sin x = 1/tanx

Since that's just

sinx/cosx = tanx flipped upsidedown.
10-10-2012, 06:00 PM
Matthew

Quote:

Originally Posted by Chippiewill

you're basically there, cos^2(x)/sinx = (cosx/sinx) * cosx = 1/tanx * cosx = cosx/tanx

You probably didn't notice that

cosx / sin x = 1/tanx

Since that's just

sinx/cosx = tanx flipped upsidedown.

ah right, makes sense :)

Thanks, +REP! :D
10-10-2012, 11:04 PM
efq

I am astonished you guys can stand that sort of Mathematics. That would stress me out to the point I would actually want to go jump off a bridge.
11-10-2012, 04:18 PM
Mr-Trainor

Quote:

Originally Posted by efq

I am astonished you guys can stand that sort of Mathematics. That would stress me out to the point I would actually want to go jump off a bridge.

I've just finished C3 trig, and it really is the most annoying part of core maths imo :(. I've never liked trig though, even at GCSE. Stats is much easier :P.
11-10-2012, 04:24 PM
Chippiewill

Quote:

Originally Posted by Mr-Trainor

I've just finished C3 trig, and it really is the most annoying part of core maths imo :(. I've never liked trig though, even at GCSE. Stats is much easier :P.

You won't be thinking that after C4 differential equations ;)
11-10-2012, 05:18 PM
Matthew

Quote:

Originally Posted by Chippiewill

You won't be thinking that after C4 differential equations ;)

haha. Did you do further maths by the way? :)
11-10-2012, 06:26 PM
Chippiewill

Quote:

Originally Posted by Matts

haha. Did you do further maths by the way? :)

Did? Doing.
12-10-2012, 03:49 PM
Mr-Trainor

Quote:

Originally Posted by Chippiewill

You won't be thinking that after C4 differential equations ;)

I can't wait! lol. I just hope there's the easy sections as well as the hard ones :P.
15-10-2012, 03:40 AM
Wig44.

Quote:

Originally Posted by Matts

Hiya
1-sin²x/sinx = cos²x/sinx

I just wanted to point out that this is essentially the end of the proof:

1-sin²x = cos²x because sin²x + cos ²x = 1, hence cos²x/sinx, which can then be written as cosx/tanx