# trig

posted by .

Given that SIN Theta = -1/sqrt(10) and theta is in quadrant 4, find sin2theta and cos2theta.

I'm not sure how to properly square the -1/sqrt10 and keep an exact answer other than decimal. Otherwise, my final answer is Sin2Theta = -.7255970691 and cos2theta = 1.632455533

• trig -

sketch a triangle in quadrant IV with opposite side 1 unit long, and the hypotenuse √10 units long.
The the adjacent side is 3 units
sinØ = -1/√10
cosØ = 3/√10 , remember the cosine is + in IV

sin 2Ø = 2sinØcosØ = 2(-1/√10)(3/√10) = -6/10 = -3/5

cos 2Ø = cos^2 Ø - sin^2Ø = 9/10 - 1/10 = 4/5

(I knew your answer was not correct since the cosine or sine of any angle cannot be bigger than 1. )

## Similar Questions

1. ### Trig

Find the exact value of sin2(theta) if cos(theta) = -sqrt 5/3 and 180 < theta < 270. A)-1/9 B)-4 sqrt 5/9 C)1/9 D)4 sqrt 5/9 B?
2. ### Calculus

Below are the 5 problems which I had trouble in. I can't seem to get the answer in the back of the book. Thanks for the help! lim (theta-pi/2)sec(theta) theta->pi/2 Answer: -1 I am not sure what to do here. lim (tan(theta))^(theta) …
3. ### simple trig

If sin(theta)=[sqrt(70)]/7 and theta is in Quadrant two, find the exact numerical value of tan theta without using a calculator. I got tan(theta)=[sqrt(294)]/42 Is that right?
4. ### easy trig

If sin(theta)=[sqrt(70)]/7 and theta is in Quadrant two, find the exact numerical value of tan theta without using a calculator. I got tan(theta)=[sqrt(294)]/42 Is that right?
5. ### Math

1. Let (-7, 4) be a point on the terminal side of (theta). Find the exact values of sin(theta), csc(theta), and cot(theta). 2. Let (theta) be an angle in quadrant IV such that sin(theta)=-2/5. Find the exact values of sec(theta) and …
6. ### Pre-Calculus

Given that SIN Theta = -1/sqrt(10) and theta is in quadrant 4, find sin2theta and cos2theta. I'm not sure how to properly square the -1/sqrt10 and keep an exact answer other than decimal. Otherwise, my final answer is 1.632455533
7. ### Trig

1. Establish the identity: sin(theta+3pi/2)=-cos(theta) 2. Find the exact value of 2(theta) if sin(theta)=5/13 3. Show that: csc2(theta)-cot2(theta)=tan(theta) 4. Find the exact value of tan(cos^-1(square root of 3/2) 5. Approximate …
8. ### Precalculus check answers help!

1.) Find an expression equivalent to sec theta sin theta cot theta csc theta. tan theta csc theta sec theta ~ sin theta 2.) Find an expression equivalent to cos theta/sin theta . tan theta cot theta ~ sec theta csc theta 3.) Simplify …
9. ### math

theta is a first quadrant angle in standard position and cos theta = 1/(sqrt10) . Find the exact value of sin theta,
10. ### Trig

Find sin2theta, cos2theta, and tan2theta for costheta = -12/13 in pi < theta < 3pi/2. My answers: 20111/24336 for tan2theta. 144/169 for cos2theta -120/338 for sin2theta

More Similar Questions