√2cos^2x+sin(π/2-x)=0 √2cos^2x+cosx=0 cosx(√2cosx+1)=0 cosx=0,x=π/2+πn cosx=-1/√2,x =+-3/4π+2πn -3/2π;-5/4π;=3/4π;-π/2;π/2;3/4π