see your previous post. You should be able to finish it off.
Check your answers to make sure they fit the original equation.
Find the value of cos2x=3/4.Find the two values of x.
0<x>pi(180)
3 answers
Can you show how to do with inverse of cos?
Picking up from oobleck's
cosx = ±√(7/8) = ±0.935
depends on your calculator.
on mine (SHARP) I do the following.
2nd cos
.935
=
to get 20.77...
I have it said on degrees, (the DRG) key, so one answer is 20.77°
Of course using your CAST rule, you know that the cosine is positive
in quads I and IV, so another answer is 360 - 20.77 ° or 339.23°
BUT, your domain was 0 < x < 180°, so we reject that answer
Going back we see that cosx = -.935
so x must be in quads II and III, but we only need quad II,
so x = 180 - 20.77 ° = 159.23
if you want your answer in radians, set the DRG to RAD
repeat the same steps, but use 2π and π instead of 360° and 180°
cosx = ±√(7/8) = ±0.935
depends on your calculator.
on mine (SHARP) I do the following.
2nd cos
.935
=
to get 20.77...
I have it said on degrees, (the DRG) key, so one answer is 20.77°
Of course using your CAST rule, you know that the cosine is positive
in quads I and IV, so another answer is 360 - 20.77 ° or 339.23°
BUT, your domain was 0 < x < 180°, so we reject that answer
Going back we see that cosx = -.935
so x must be in quads II and III, but we only need quad II,
so x = 180 - 20.77 ° = 159.23
if you want your answer in radians, set the DRG to RAD
repeat the same steps, but use 2π and π instead of 360° and 180°
1 answer