Posted by Jiskhaa on Monday, April 8, 2013 at 2:31am.
Find the exact values of sin 2 theta, cos 2 theta and tan 2thea using the double angle formula
sin theta = 3/4 , pi/2 < theta < pi

Trig  Reiny, Monday, April 8, 2013 at 7:59am
given: sinØ = 3/4, and Ø is in quadrant II
then by Pythagoras, y= 3, x = ? , r = 4
x^2 + 9 = 16
x = ±√5 , but in II x = √7
so cosØ = √7/4
sin 2Ø = 2sinØcosØ
= 2(3/4)(√7/4) = 6√7/16
= 3√7/8
cos 2Ø = cos^2 Ø  sin^2 Ø = 7/16  9/16
= 2/16
=  1/8
tan 2Ø = sin 2Ø / cos 2Ø
= (3√7/8) / (1/8)
= 3√7
Answer This Question
Related Questions
 Calculus  I wanted to confirm that I solved these problems correctly (we had to...
 Math  1. Let (7, 4) be a point on the terminal side of (theta). Find the exact...
 trig  If sin theta is equal to 5/13 and theta is an angle in quadrant II find ...
 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 ...
 Trigonometry  Prove the following identities: 1. (tan theta  sin theta)^2 + (1...
 Trigonometry  Prove the following identities: 1. (tan theta  sin theta)^2 + (1...
 trig  Find csc(theta), tan (theta), and cos (theta), where theta is the angle ...
 Trig  1. Establish the identity: sin(theta+3pi/2)=cos(theta) 2. Find the exact...
 trig  the terminal side of angle theta in standard position lies on the line ...
More Related Questions