Saturday

December 20, 2014

December 20, 2014

Posted by **Priya** on Thursday, May 1, 2008 at 4:46pm.

Yes, thank you again Reiny!

My next question is to find sin theta and cos theta.

cos 2theta = 1/3 and pi less than or equal to 2theta less than or equal to 2pi

I hope Im not overburdening you with question:/

- trig -
**Reiny**, Thursday, May 1, 2008 at 5:04pm<<I hope Im not overburdening you with question:/>>

lol, I love trig and do these kind of questions for recreation.

for this one you will need to know

1. sin2A = 2sinAcosA, and

2. cos2A = cos^2 A - sin^2 A

or 2cos^2 A -1

or 1 - 2sin^2 A

I will do the first, you do the second

cos2A = 1-2sin^2A

1/3 = 1 - 2sin^2 A

2 sin^2 A = 1 - 1/3

sin^2 A = 1/3

sinA = ±1/√3 (I used A instead of theta)

Can we use both ± ?

2theta is in either I or IV

then theta is in either I or II, but the sine in both of these is positive, so

sinA = +1/√3 only.

you try the second one.

**Answer this Question**

**Related Questions**

Calculus - I wanted to confirm that I solved these problems correctly (we had to...

Maths- complex numbers - Find tan(3 theta) in terms of tan theta Use the formula...

math - I have a question I have been working on since yesterday and I am not ...

precalc h - sin(theta)/1-cos(theta) + 1-cos(theta)/sin(theta) = 2csc(theta) That...

trig 26 - simplify to a constant or trig func. 1. sec Ču-tan Ču/cos Čv+sin Čv ...

science - Sitting on a horizontal track is a mass of 10kg. One end of the track ...

Trigonometry - Thank you STEVE!!!!! Suppose that Cos (theta) = 1/square root 2 ...

math (trig) - if cos 2 theta = -(1/3) and theta is in Quadrant 2, find sin theta...

Precalculus check answers help! - 1.) Find an expression equivalent to sec theta...

Precalculus check answers help! - 1.) Find an expression equivalent to sec theta...