2sin^2(x)-sin(x)=3

**pd1dish** · February 18th 2008, 05:15 PM

2sin^2(x)-sin(x)=3 find for all values of x. this is pre-calc stuff.

**topsquark** · February 18th 2008, 05:19 PM

Originally Posted by pd1dish

2sin^2(x)-sin(x)=3 find for all values of x. this is pre-calc stuff.

This is a quadratic equation problem.

Let $y = sin(x)$ . Then your equation becomes:
$2y^2 - y = 3$

Solve this for y and then take the inverse sine of the two answers.

-Dan

**pd1dish** · February 18th 2008, 05:26 PM

what would i do from there...i have no clue what is going on in my pre-calc class right now so if some1 can just post every step, that would be really helpful and i have a couple more problems similar to this one and me seeing each step will help me with those.

**mr fantastic** · February 18th 2008, 05:32 PM

Originally Posted by pd1dish

what would i do from there...i have no clue what is going on in my pre-calc class right now so if some1 can just post every step, that would be really helpful and i have a couple more problems similar to this one and me seeing each step will help me with those.

Do you know how to solve a quadratic equation?
Do you know that $-1 \leq \sin x \leq 1$ and so there are no real solutions to something like $\sin x = \frac{3}{2} \,$ ?
Do you know how to solve $\sin x = -1\,$ ?

**pd1dish** · February 18th 2008, 05:34 PM

w/e...u guys arent helping. all i wanted was a step by step process. im going to a different site that actually gives u the answer instead of making me figure it out.

**mr fantastic** · February 18th 2008, 05:46 PM

Originally Posted by pd1dish

w/e...u guys arent helping. all i wanted was a step by step process. im going to a different site that actually gives u the answer instead of making me figure it out.

You've been given quite a bit of help, actually. I'm sorry that the effort required of you to take that help on board is too great.

Simple yes or no answers to my questions would have been useful in pinpointing your exact troubles.

Your mathematical difficulties seem to extend beyond trigonometry - you're encouraged to get as much extra help as possible from your instructor.

And the answer is $x = \frac{(4n+3) \pi}{2}$ where n is an integer.

**Jhevon** · February 18th 2008, 05:50 PM

Originally Posted by pd1dish

w/e...u guys arent helping. all i wanted was a step by step process. im going to a different site that actually gives u the answer instead of making me figure it out.

they are helping more than you know. helping you figure out things for yourself is better. when you're in an exam, who is the one who's going to have to figure stuff out? you might as well get used to it from now

**Krizalid** · February 18th 2008, 06:08 PM

Originally Posted by pd1dish

w/e...u guys arent helping.

They actually did.

Originally Posted by pd1dish

all i wanted was a step by step process.

This depends, you just posted the question and you didn't even show a progress. Do you want a coke, cigarette, something else while someone is giving you a full solution?

Originally Posted by pd1dish

im going to a different site that actually gives u the answer instead of making me figure it out.

It's not a duty to give you a full solution, from a beginning you didn't specify anything.

Of course, the door is big enough. (Do you think that you scare us with such comment, rating's site will decay?)

**Charbel** · February 20th 2008, 02:47 AM

Originally Posted by mr fantastic

You've been given quite a bit of help, actually. I'm sorry that the effort required of you to take that help on board is too great.

Simple yes or no answers to my questions would have been useful in pinpointing your exact troubles.

Your mathematical difficulties seem to extend beyond trigonometry - you're encouraged to get as much extra help as possible from your instructor.

And the answer is $x = \frac{(2n+1) \pi}{2}$ where n is an integer.

Upon doing the maths

2 sin^2(x) - sin(x) = 3

2 sin ^2(x) - sin(x) - 3 = 0

let sin(x)=y

2y^2 - y - 3 = 0

(2y-3)(y+1) = 0

therefore

sin x = 3/2 and -1

since -1 <= sin <= 1

sin x = -1

x = sin^-1 (-1)

x = 3pi / 2 + 2pi(n) where n is an element of Z

sorry if im wrong =[ but like that seems right XD

I think your answer is solved for = 1 not = 3

edit .. or you used 1 instead of -1 ... ?

sorry if im wrong >.>

femmekarammel · March 5th 2008, 05:38 PM

I'm not even taking trig and this is an easy problem. People: learn to do some work instead of having other people do it for you.

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