There are several missing operators (that I assume should be multiplication operators), and all the applidable operators should be element-wise, so (.*) instead of (*) and (./) instead of (/).
x=[0.2:0.1:0.7];
y1=1./((x/400 +(1-x)/80) .* (1./x+(0.5.*(1-x))));
y2 =1./(1/40) .* (1-x)+(1./400).*(x);
figure
plot(x, y1, x, y2)
grid
legend('y_1','y_2', 'Location','best')
.
