Posted by denise on Sunday, July 24, 2011 at 9:01pm.
solve the equation 4cos^2x1=0

precal 2  Reiny, Sunday, July 24, 2011 at 10:02pm
cos^2x = 1/4
cosx = ± 1/2
do you know an angle x , so that cosx = 1/2 ???
and by the CAST rule, isn't that angle in any of the 4 quadrants?
hint: cos60° = 1/2