Posted by Joe on Wednesday, July 13, 2011 at 4:10pm.
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  Reiny, Wednesday, July 13, 2011 at 7:08pm
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. )
Answer This Question
Related Questions
 PreCalculus  Given that SIN Theta = 1/sqrt(10) and theta is in quadrant 4, ...
 Trig  Find sin2theta, cos2theta, and tan2theta for costheta = 12/13 in pi <...
 easy trig  If sin(theta)=[sqrt(70)]/7 and theta is in Quadrant two, find the ...
 simple trig  If sin(theta)=[sqrt(70)]/7 and theta is in Quadrant two, find the ...
 math  theta is a first quadrant angle in standard position and cos theta = 1/(...
 Trig  Find sin2theta, cos2theta if csctheta=13/12 and lies in quadrant II. ...
 Trig  Find the exact value of sin2(theta) if cos(theta) = sqrt 5/3 and 180 <...
 Trig  1. Establish the identity: sin(theta+3pi/2)=cos(theta) 2. Find the exact...
 Calculus  Below are the 5 problems which I had trouble in. I can't seem to get ...
 Math  1. Let (7, 4) be a point on the terminal side of (theta). Find the exact...
More Related Questions