# Homework Help: Another trig. question

1. Dec 11, 2009

### ibysaiyan

1. The problem statement, all variables and given/known data
Given that 5sec^2+3tan^2 = 9
find sinx value

2. Relevant equations
trig. identities

3. The attempt at a solution
i started off by subbing. in sec2= 1+tan^2
=>
5(1+tan^2)+3tan^2= 9
5+8tan^2x = 9
8tan^2 = 4
tan^2 = 1/2 <--- no idea of this bit, as i am supposed to find sin x value =/ , hmm i even wonder if this right.

2. Dec 11, 2009

### rock.freak667

Yes it is correct. Take the square root and find the angles for the two values.

3. Dec 11, 2009

### ibysaiyan

tanx= $$\sqrt{}1/2$$
x= inverse. sin $$\sqrt{}1/2$$ is that how i get values for sin?

4. Dec 11, 2009

### rock.freak667

You will have two values, x2=a ⇒ x=±√a

Also if tanx=y, then x=tan-1(y). Where did you get inverse sine from?

5. Dec 11, 2009

### ibysaiyan

Exactly lol thats what i thought.. the question wants me to get sinx values if possible :9.

6. Dec 11, 2009

### rock.freak667

Sorry, I mis-read the question. While you can just find the values for x, and then find sinx.

You can also use tanx=sinx/cosx and then use cos2x=1-sin2x and solve for sinx.

7. Dec 12, 2009

### ibysaiyan

ah k, thanks for helping me out :).