# Does this Look right?

• Nov 13th 2012, 05:49 PM
M670
Does this Look right?
Suppose and http://webwork.mathstat.concordia.ca...c4ab36f8c1.png is negative. Here are some small variations on the previous problems:
http://webwork.mathstat.concordia.ca...b69be1bdf1.png
http://webwork.mathstat.concordia.ca...96990ee631.png
http://webwork.mathstat.concordia.ca...d042b0e5f1.png
http://webwork.mathstat.concordia.ca...846bc07dc1.png
http://webwork.mathstat.concordia.ca...85572f1991.png

Which one of the two addition formals would put me on the right way?
sin(u-pi)=sin(u)cos(pi)-cos(u)sin(pi)
or
sin(-(12/13)-pi)= sin-(12/13)cos(pi)-cos-(12/13)sin(pi)?
• Nov 13th 2012, 05:58 PM
MarkFL
Re: Does this Look right?
I would use:

$\sin(u)=-\sqrt{1-\cos^2(u)}$

$\sin(u-\pi)=-\sin(\pi-u)=-\sin(u)$

$\cos(u-\pi)=\cos(\pi-u)=-\cos(u)$

$\sin\left(u-\frac{\pi}{2} \right)=-\sin\left(\frac{\pi}{2}-u \right)=-\cos(u)$

$\cos\left(u-\frac{\pi}{2} \right)=\cos\left(\frac{\pi}{2}-u \right)=\sin(u)$
• Nov 13th 2012, 06:35 PM
M670
Re: Does this Look right?
Quote:

Originally Posted by MarkFL2
I would use:

$\sin(u)=-\sqrt{1-\cos^2(u)}$

$\sin(u-\pi)=-\sin(\pi-u)=-\sin(u)$

$\cos(u-\pi)=\cos(\pi-u)=-\cos(u)$

$\sin\left(u-\frac{\pi}{2} \right)=-\sin\left(\frac{\pi}{2}-u \right)=-\cos(u)$

$\cos\left(u-\frac{\pi}{2} \right)=\cos\left(\frac{\pi}{2}-u \right)=\sin(u)$

Thank You very much, So the initial cos (u)=5/13 has nothing to do with the other problems? I thought I had to relate each one to the original somehow
• Nov 13th 2012, 06:37 PM
M670
Re: Does this Look right?
But the other problem is when I input your answers the program tells me variable "u" is not defined in this context?
meaning these answers it will consider wrong
• Nov 13th 2012, 07:17 PM
MarkFL
Re: Does this Look right?
You are given the value of cos(u), then from this you may find sin(u) using the first formula, and since you now have sin(u) and cos(u), the rest come from that.
• Nov 13th 2012, 07:39 PM
M670
Re: Does this Look right?
but sin(u) is -(12/13)
• Nov 13th 2012, 07:42 PM
M670
Re: Does this Look right?
Which would mean sin(u-pi) should be Sin(u-pi)= sin-(12/13)cos(pi)-cos-(12/13)(sin(pi)
• Nov 13th 2012, 08:15 PM
MarkFL
Re: Does this Look right?
If sin(u) = -12/13, then -sin(u) = 12/13.