x Turn on thread page Beta
 You are Here: Home >< Maths

# Trig Equation which I do not know how to solve watch

1. If anyone could help me with this it would help, thanks.

2(sinx^2) +2sinxcosx - 1 = 0
2. How can you rewrite 2sinxcosx to get it in terms of sin?
3. Sin(A+B)=SinACosA+CosBSinB or something like that, we havent done that yet at college.
4. (Original post by ilovedubstep)
Sin(A+B)=SinACosA+CosBSinB or something like that, we havent done that yet at college.
you need to use it.
2sinxcosx = sin(2x)

When you write 2(sinx^2), what do you mean? 2(sinx)² ( = 2sin²x )?
or 2sin(x²).
5. One way to do it:

s= sin x
c= cos x

(2s^2-1)^2 = 4s^2c^2
(2s^2-1)^2 = 4s^2(1-s^2)

subtitute:
y=s^2

(2y-1)^2 = 4y(1-y)

4y^2-4y+1 =4y-4y^2
8y^2 - 8y + 1 = 0

solve for y.

x = arcsin( sqrt(y) )
6. (Original post by ilovedubstep)
If anyone could help me with this it would help, thanks.

2(sinx^2) +2sinxcosx - 1 = 0
Write this as:

Then note that and .
7. (Original post by Melanie-v)
you need to use it.
2sinxcosx = sin(2x)

When you write 2(sinx^2), what do you mean? 2(sinx)² ( = 2sin²x )?
or 2sin(x²).

2sin²x

so cosxsinx = (sin(2x))/2 ?

This leads to another problem... How do I solve

4sin²x + sin(2x) -2 ?

The answer is 45 dont worry I've solved it now!

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 23, 2011
Today on TSR

### Loughborough better than Cambridge

Loughborough at number one

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams