SOLUTION: Hi can someone help me with this problem please? THANK YOU! Find the exact value of cos(2 theta) cos(theta)=-15/17 and theta terminates in QII. a.-2

Algebra.Com
Question 1077273: Hi can someone help me with this problem please? THANK YOU!
Find the exact value of cos(2 theta)
cos(theta)=-15/17 and theta terminates in QII.
a.-240/289
b.161/289
c.120/289
d.16/17
Found 2 solutions by htmentor, MathTherapy:
Answer by htmentor(1343)   (Show Source): You can put this solution on YOUR website!
Given that cos(t) = -15/17, we know the adjacent side is 15 (QII) and the hypotenuse is 17.
Let the opposite side by x. Then sin(t) = x/17
From the Pythagorean theorem we know that x^2 = 17^2 - 15^2
We can make use of the identity, cos(2t) = cos^2(t) - sin^2(t)
sin^2(t) = x^2/17^2 = (17^2-15^2)/17^2 = 1 - (15/17)^2
Therefore, cos(2t) = (-15/17)^2 - [1-(15/17)^2] = (450-289)/289 = 161/289
Ans: b
Answer by MathTherapy(10551)   (Show Source): You can put this solution on YOUR website!

Hi can someone help me with this problem please? THANK YOU!
Find the exact value of cos(2 theta)
cos(theta)=-15/17 and theta terminates in QII.
a.-240/289
b.161/289
c.120/289
d.16/17


 ------ Substituting 





 

RELATED QUESTIONS


Can someone PLEASE help me with this problem?

Find the exact value of cos(2theta)... (answered by jim_thompson5910)

Can someone PLEASE help me with this problem? Thank you!

If tan(theta)=9/8 and... (answered by scott8148)

Can someone please help me with this problem?
/
If tan theta = 5/12, what is the value... (answered by stanbon)

Hi can someone help me with this problem please? THANK YOU! 

The range of a projectile  (answered by Boreal)

Please help me solve this question:

1.Suppose cos theta = - √3/2 is the second... (answered by lwsshak3)

Use sin of theta = -8/17
and theta lies on quadrant III

find the exact value of a)... (answered by Alan3354)

Please help me solve this question:

Suppose cos theta = - √3/2 and theta is the... (answered by lwsshak3)

hello :
 i really could use some help with this problem. i am a little confused with... (answered by stanbon)

Step by step expanation?
Given cos (theta) = -15/17 and 180 < theta < 270, find the... (answered by solver91311)