1.
2sin^2(x)+5cos(x)-4=0
2sin^2(x)-4sin^2(x)-4cos^2(x)+5cos(x)=0
-2sin^2(x)-4cos^2(x)+5cos(x)=0
-2(1-cos^2(x))-4cos^2(x)+5cos(x)=0
-2-2cos^2(x)+5cos(x)=0
cos(x)=t (-1-2t^2+5t-2=0
2t^2-5t+2=0
D=25-16=9
t1=(5+3)/4=2
t2=(5-3)/4=1/2
cos(x)=1/2
x=pi/3+2pi*n, n∈Z
x= -pi/3+2pi*n, n∈Z
2.
r=3 см; h=4 см
S(бок)=pi*r*l=⊕
l=sqrt(r^2+h^2)=sqrt(9+16)=5
⊕=3*5*pi=15pi см^2