

Giải pt
a)2cos2x + cos^2 x/2 -10cos(5pi/2-x)+7/2=1/2cosx
b) cos5x*cosx = cos4x* cos2x +3cos^2+1
c) cos4x-3*(1-tan^2)/(1+tan^2) +2=0
a)2cos2x + cos^2 x/2 -10cos(5pi/2-x)+7/2=1/2cosx
b) cos5x*cosx = cos4x* cos2x +3cos^2+1
c) cos4x-3*(1-tan^2)/(1+tan^2) +2=0