# Math (Find the Value)

posted by .

If 0 < (theta) and cos(theta)=0.5, then what is the value of cos(2theta)?

• Math (Find the Value) -

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).

• Math (Find the Value) -

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.

## Respond to this Question

 First Name School Subject Your Answer

## Similar Questions

1. ### math

There are no typos and no work b/c I don't know how to do them. Thanks. 1)Find cos theta if sin theta=3/5 and 90 degrees<theta<180 degrees. A)4/5 B)-4/5 C)square root of 34/5 D)-square root of 34/5 I chose A 2)Simplify:1-csc^2theta/cot^2theta …
2. ### Algebra II

Which of the following expressions are not equal to 1?
3. ### Pre-Calculus-check answers

If cos theta = 0.8 and 270<theta<360, find the exact value of sin 2theta a) -0.96 b) -0.6 c) 0.96 d) 0.28 Answer: b 2) If csc theta = -5/3, and theta has its terminal side in Quadrant III, find the exact value of tan 2theta a)24/25 …
4. ### Calculus

I wanted to confirm that I solved these problems correctly (we had to convert the polar curves to Cartesian equations). 1.rcos(theta)=1 x=1 2.r=2*sin(theta)+2*cos(theta) r^2=2rsin(theta)+2rcos(theta) x^2+y^2=2y+2x (a little unsure …
5. ### Pre Calc.

Use the sum or difference identity to find the exact value of sin255 degrees. My answer: (-sqrt(2)- sqrt(6)) / (4) Find the value of tan (alpha-beta), if cos alpha= -3/5, sin beta= 5/13, 90<alpha<180, and 90<beta<180. My …
6. ### 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 …
7. ### Precalculus 2

Similiarly to a question I asked previously I took the same approach. the problem is: what value(s) of theta solve the following equation?
8. ### trig

given that 1/2pi<theta<pi and sin theta=1/5, use appropriate trigonometric formulas to find the exact values of the following (i) cos(2theta) (ii) cos theta (iii) sin(2theta)
9. ### Math

sin theta = 8/17 and theta is in the second quadrant. Find sin(2theta),cos(2theta),tan(2theta) exactly sin(2theta) cos(2theta) tan(2theta) sin(2theta) would it be 2 x (8/17) cos(2theta) would be 2 x (15/17) tan(2theta) would be 2 x …
10. ### Math

Fin the value of Theta if sec theta=3 I inverted the value of sec theta to get cos theta=1/3 I then said Theta=cos-1 (1/3) Is thus correct?

More Similar Questions