Finding xy coordinates of obtuse and acute triangle

[amit25]

This might seem easy, but I am sort of rusty on the math since i haven't taken a math course in a while.

Homework Statement

A 2 meter long bar lies in the xy plane with one end at the origin. find position at the xy plane of the other?

end point of the bar if the angle the bar makes with the x-axis is the followin
a) 2pi/3
b) 120 degree
c) 30 degree

Homework Equations

The Attempt at a Solution

do i use x=2cosx y=2sinx ? for the 30 degree angle one i used
but when i get to 120degrees i used the sin law but somethin seems off

 

[Mentallic]

This might seem easy, but I am sort of rusty on the math since i haven't taken a math course in a while.

Homework Statement

A 2 meter long bar lies in the xy plane with one end at the origin. find position at the xy plane of the other?

end point of the bar if the angle the bar makes with the x-axis is the followin
a) 2pi/3
b) 120 degree
c) 30 degree

Homework Equations

The Attempt at a Solution

do i use x=2cosx y=2sinx ? for the 30 degree angle one i used
but when i get to 120degrees i used the sin law but somethin seems off

For the 120^o and $2\pi / 3$ angles, they're obtuse (between 90^o and 180^o) so you need to look into the second quadrant (this means the cos(x) value will be negative, while the sin(x) value will still be positive, but you need to reconsider what the value of x is because you're now dealing with a triangle that isn't using the angle you started with).

Here's an illustration, notice $$\frac{\pi}{3}=\pi-\frac{2\pi}{3}$$
Which in degrees is equivalent to $60^o=180^o-120^o$

http://img835.imageshack.us/img835/6619/trianglehelp.png