Question 805646
solve the equation in Radians for all exact solutions where appropriate. Round approximate answer in radians to four decimal place. write answer using the least possible non-negative angle measures. 
cos x (5 cos x - 1) = 3
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cos x (5 cos x - 1) = 3
5cos^2(x)-cos(x)=3
5cos^2(x)-cos(x)-3=0
solve for cos(x) by quadratic formula:
{{{cos(x) = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
a=5, b=-1, c=-3
ans:
cos(x)=-0.6810
use calculator inverse cos key set to radians
x=2.3199+2&#960;k, 3.9633,+2&#960;k, k=integer (In quadrants II and III where cos<0)
or
cos(x)=0.8810
use calculator inverse cos key set to radians
x=0.4928+2&#960;k, 5.7904,+2&#960;k, k=integer (In quadrants I and IV where cos>0)