alcazar

iTrader: (2)

Struggling through Trig identities and their solutions, I've come across this:


Cos (x +π/2) = 1/2 (π is "pi", not very well produced on this computer).


I have to solve it for 0 <= x <= 360.


It's doing my head in, I keep getting values of either π/6, or 5π/6


The actual answers should be 7π/6 and 11π/6


Any body help before my head explodes?

funkmasterjay

Sorry dude, this looks beyond the A level pure maths and mechanics I did 15 years ago.

Best of luck.

ReallyReallyGoodMeat

cos(x+pi/2) = 1/2
cos(pi/3 or 60deg) = 1/2 and cos (-pi/3 or -60deg) = 1/2
therefore for the first case...
x+pi/2 = pi/3 (60deg = 1/3pi)
x = pi/3 - pi/2
x = 2pi/6 - 3pi/6
x = -pi/6
normalize for 0 < x < 360 by adding 2pi
x = 11/6 pi
Repeat for the other case.

*Did A-level pure maths and mechanics 15 years ago

funkmasterjay

I have a great admiration for those that still remember and apply their maths. I remember bits, but as I don't use it, I'm now thick! Lol.

ReallyReallyGoodMeat

I still use some of it for my day-job so if it wasn't for that I'd probably be the same

alcazar

iTrader: (2)

DAMN!!! I was nearly there!

Thanks a lot for that.

speedking

cos(A+B) = cosAcosB - sinAsinB
=cos(x)cos(π/2) - sin(x)sin(π/2)
as cos(π/2) = 0 and sin(π/2) = 1
=-sin(x)

so, 1/2 = -sin(x)
x = arcsin(-1/2)
x = -π/6

as above, add 2π to get 11π/6

Tony Harrington

iTrader: (8)

1 + 1 = 3

alcazar

iTrader: (2)

LOL, some of it comes over like that, doesn't it.
Black magic, it is, I tell you.......

finalzero

I am a calculator kid unfortunately but never needed to do maths at that level, wish I had.

Strange being a software developer you would have thought I would have a need to learn maths but you get by without it, had a go at some uni courses and found it to actually be a a pure form of programming (especially that stuff you're doing).

ReallyReallyGoodMeat

Nice