1. ## Basic trig

I just get confused by something very basic,

Imagine we got cos 2x = something

And the angle lies between 0 and 180

so to solve it, i gotta multiply the range by 2 right ?

I mean when the equation gets complex, how to do these kind of things...

Do i solve for 2x first then divide, or find x and find it in its quadrant, sorry, i dont really get it...

like i had this number sin2x = 1/2

range was -180 to 180

so you solve for 2x which gives you 30

so x = 15 right,

muliplying the range gives me - 360 to 360

the answer is 15 75 -165 -105

can someone explain it to me, im a bit confused...

2. Originally Posted by ramzel
I just get confused by something very basic,

Imagine we got cos 2x = something

And the angle lies between 0 and 180

so to solve it, i gotta multiply the range by 2 right ?

I mean when the equation gets complex, how to do these kind of things...

Do i solve for 2x first then divide, or find x and find it in its quadrant, sorry, i dont really get it...

like i had this number sin2x = 1/2

range was -180 to 180

so you solve for 2x which gives you 30

so x = 15 right,

muliplying the range gives me - 360 to 360

the answer is 15 75 -165 -105

can someone explain it to me, im a bit confused...
$\sin(2x) = \frac{1}{2}$

note that the value of 2x must be in quads I and II ...

$-180 < x < 180$

$-360 < 2x < 360$

between 0 and 360 ... $2x = 30 \, , \, 150$

$x = 15 \, , \, 75$

and between 0 and -360 ...

$2x = -210 \, , \, -330$

$x = -105 \, , \, -165$

3. Thank you