Posted by Parker on Friday, August 14, 2009 at 2:46pm.
First solve cos(theta)=0.5
Step 1: Where is the cosine of theta equal to 0.5? Think about your memory angles or special triangles.
Step 2: Now double the angles found in step 1, and take the cosine of the new angle you found. (Both answers should be the same).
Another approach using double angle identities.
cos(2A)=cos²(A)-sin²(A)=2cos²(A)-1
You will find cos(2A) by subtituting the value of cos(A) in the above equation.
Related Questions
Pre Calc. - Use the sum or difference identity to find the exact value of sin255...
math - There are no typos and no work b/c I don't know how to do them. ...
Pre-Calculus-check answers - If cos theta = 0.8 and 270<theta<360...
trig - given that 1/2pi<theta<pi and sin theta=1/5, use ...
Math - There are no typos and no work b/c I don't know how to do them. ...
Trig - 1. Establish the identity: sin(theta+3pi/2)=-cos(theta) 2. Find the exact...
Math - 1)Find cos theta if sin theta=3/5 and 90 degrees<theta<180 ...
Trig - Find the exact value of sin2(theta) if cos(theta) = -sqrt 5/3 and 180 &...
Algebra II - Multiple Choice (theta) means the symbol 0 with the dash in it. 1.)...
trig - given that cos(theta)= (3/5) and sin (theta)<0, find sin(2 theta) ...
For Further Reading
