# Trig

• Jan 15th 2009, 01:50 PM
alpina
Trig
Can somebody help me do these please.o (greater or equal to) y and (less than or equal to) 360 degrees.

1. sin(x/2)= √3/2

2. 2sin^2(x) - 7sin(x) = -3 when o (greater or equal to) x and (less than or equal to) 360 degrees.

3. and most importantly sin2(y)= 4y when o (greater or equal to) y and (less than or equal to) 360 degrees.

Thanks.

• Jan 15th 2009, 02:00 PM
Last_Singularity
Quote:

Originally Posted by alpina
Can somebody help me do these please.o (greater or equal to) y and (less than or equal to) 360 degrees.

1. sin(x/2)= √3/2

2. 2sin^2(x) - 7sin(x) = -3 when o (greater or equal to) x and (less than or equal to) 360 degrees.

3. and most importantly sin2(y)= 4y when o (greater or equal to) y and (less than or equal to) 360 degrees.

Thanks.

1. Let $\displaystyle y = \frac{x}{2}$. So you're solving
$\displaystyle sin(y) = \sqrt{3}/2$. Find the value of $\displaystyle y$ and then convert it back to $\displaystyle x$

2. Let $\displaystyle sin(x) = y$. So you're solving
$\displaystyle 2y^2 - 7y + 3 = 0$. Solve that for $\displaystyle y$ and then solve the equation $\displaystyle sin(x) = y$

3. I can't read your notation here. Is it $\displaystyle sin(2y)$ or $\displaystyle sin^2 y$?
• Jan 15th 2009, 02:49 PM
alpina
Quote:

Originally Posted by Last_Singularity
1. Let $\displaystyle y = \frac{x}{2}$. So you're solving
$\displaystyle sin(y) = \sqrt{3}/2$. Find the value of $\displaystyle y$ and then convert it back to $\displaystyle x$

2. Let $\displaystyle sin(x) = y$. So you're solving
$\displaystyle 2y^2 - 7y + 3 = 0$. Solve that for $\displaystyle y$ and then solve the equation $\displaystyle sin(x) = y$

3. I can't read your notation here. Is it $\displaystyle sin(2y)$ or $\displaystyle sin^2 y$?

thanks for your reply, and it is $\displaystyle sin(2y)$. first time doing math on computer =)), sorry.
• Jan 15th 2009, 04:54 PM
Last_Singularity
So for $\displaystyle sin(2y)= 4y$, let $\displaystyle x=2y$. Then we get:
$\displaystyle sin(x) = 2x$

Use a graphing calculator of some sorts to find where $\displaystyle sin(x) - 2x = 0$

Then divide by 2 to get your value of $\displaystyle y$
• Jan 16th 2009, 07:40 AM
alpina
still don't really understand how to do it right