abbyl94
cos theta = 4/5, 0˚< theta < 90˚ use the information given to find sin2theta, cos2theta, and tan 2theta
Delete
Share
This Question is Closed
anonymous
Best Response
You've already chosen the best response.
0
you need \(\sin(\theta)\) so compute these
do you know how to find it?
abbyl94
Best Response
You've already chosen the best response.
0
the identities?
anonymous
Best Response
You've already chosen the best response.
0
|dw:1358823887705:dw|
alanli123
Best Response
You've already chosen the best response.
0
sin 2 theta = 2 sin theta cos theta
cos 2 theta = 2 cos ^2 theta - 1
tan 2 theta = sin 2 theta / cos 2 theta
abbyl94
Best Response
You've already chosen the best response.
0
do i plug in 4/5 where theta is?
Azteck
Best Response
You've already chosen the best response.
1
If costheta=4/5 then sintheta= 3/5
\[\sin2\theta=2\sin\theta \cos\theta\]
anonymous
Best Response
You've already chosen the best response.
0
there is a picture of an angle whose cosine is \(\frac{4}{5}\) you find the third side by pythagoras, or recalling the 3 - 4 - 5 right triangle
this tells you \(\sin(\theta)=\frac{3}{5}\)
abbyl94
Best Response
You've already chosen the best response.
0
oh okay
abbyl94
Best Response
You've already chosen the best response.
0
so 2 sin theta = 2 sin 3/5 cos 4/5
anonymous
Best Response
You've already chosen the best response.
0
no do not make that mistake, it is a common one
do not use \(\theta=\frac{4}{5}\) use \(\cos(\theta)=\frac{4}{5}\) so \[\sin(2\theta)=2\times \frac{4}{5}\times \frac{3}{5}\]
anonymous
Best Response
You've already chosen the best response.
0
no not the cosine and sine of those numbers, those numbers ARE the cosine and sine
anonymous
Best Response
You've already chosen the best response.
0
use the numbers themselves, they are your sines and cosines
abbyl94
Best Response
You've already chosen the best response.
0
okay thank you!
anonymous
Best Response
You've already chosen the best response.
0
your good now right?
abbyl94
Best Response
You've already chosen the best response.
0
im still confused a little ..