Read about matlab element by element operations:
R1=1000 %Ohm%
C1=0.000000032;%F%
R2=1000 %Ohm%
C2=0.000000032;%F%
x=linspace(0,100,100)
y= 20*log(abs(1./(R1*R2*C1*C2))./((2*pi*(x)).*(2*pi*(x))+(2*pi*(x)).*(1/(R1*C1))+(1/(R2*C1))*(1/(R2*C2)))) ;
semilogx (x,y);
xlabel("frequency");
ylabel("y(x)");
title("x");