Question

cos^2x-5cosx+4<=0 поооомгииитте

Answer 1

cosx=a
a²-5a+4≤0
a1+a2=5 U a1*a2=4⇒a1=1 U a2=4
1≤a≤4
1≤cosx≤4
|cosx|≤1⇒cosx=1
x=2πn,n∈z