cos x= -1/2 (-pi
2007-06-12 03:58:10 · 3 answers · asked by meg 1 in Science & Mathematics ➔ Mathematics
Take the inverse cosine of both sides.
acos (cos x) = acos (-1/2)
x = acos (- 1/2).
This may be difficult to evaluate exactly (at least, if you don't know your unit circle....) But if you remember,
cos (-2π/3) = -1/2
therefore: x = -2π/3
"Elementary, my dear Watson...."
~W.O.M.B.A.T.
2007-06-12 04:16:21 · answer #1 · answered by WOMBAT, Manliness Expert 7 · 1⤊ 0⤋
Draw a 30-60-90 degree triangle. The hypotenuse is represented with a 2, the -1 is opposite the 30 degree angle. Since this is a 30-60-90 degree triangle the side opposite the 60 degree angle is radical 3. You have to find which angle on the trangle gives you -1/2 which is 60 degrees, and in radian mode it is -pi/3.
you can also simply use a calculator and evaluate arc cosine or inverse of cosine. i'm sure you know how to do this.
hope that helped.
2007-06-12 04:07:05 · answer #2 · answered by Carpe Diem (Seize The Day) 6 · 0⤊ 1⤋
use the inverse...
if you have a graphing calculator it's easy!
sory can't explain....
2007-06-12 04:07:04 · answer #3 · answered by -uNkNoWn- 1 · 0⤊ 1⤋