Help about function with if statement

I have problem with creating function. I don´t know how to use command function properly. Can you guys tell me where I was wrong it will be very helpful

function [y]=task1(x)

if x>=8

       y = 14*(5*x)^(1/2)+9;
end

if (-1<=x<8)

         y=9*x +9;
end

if (x<-1) y=9;

end