L ladyazpy New member Joined Mar 1, 2005 Messages 31 Apr 26, 2006 #1 How can i solve this without a calculator? Cos ^-1 (1/2) Cos ^-1 (-1/2)

tkhunny Moderator Staff member Joined Apr 12, 2005 Messages 10,214 Apr 26, 2006 #2 If \(\displaystyle a = cos^{-1}(1/2)\), then cos(a) = 1/2. That value should be on any chart of values that you should memorize.

If \(\displaystyle a = cos^{-1}(1/2)\), then cos(a) = 1/2. That value should be on any chart of values that you should memorize.

pka Elite Member Joined Jan 29, 2005 Messages 8,670 Apr 26, 2006 #3 Do you know a standard acute angle, Θ, such cos(Θ)=1/2 ? Then the equivalent angle in the second quadrant \(\displaystyle \cos (\pi - \theta ) = - 1/2\).

Do you know a standard acute angle, Θ, such cos(Θ)=1/2 ? Then the equivalent angle in the second quadrant \(\displaystyle \cos (\pi - \theta ) = - 1/2\).