I try to run a quadric Solution code in F# and always have an error

This is a part of The code :

let quadratic a b c=

let y=sqrt(b*b-4.0*a*c)

let y=sqrt(b*b-4.0*a*c)

^^^^

stdin(2,1): warning FS0058: possible incorrect indentation: this token is offside of context started at position (1:1). Try indenting this token further or using standard formatting conventions

let y=sqrt(b*b-4.0*a*c)

^^^^

stdin(2,1): warning FS0058: possible incorrect indentation: this token is offside of context started at position (1:1). Try indenting this token further or using standard formatting conventions

(-b+y)/(2.0*a),(-b-y)(2.0*a);;

(-b+y)/(2.0*a),(-b-y)(2.0*a);;

^^

stdin(3,1): warning FS0058: possible incorrect indentation: this token is offside of context started at position (1:1). Try indenting this token further or using standard formatting conventions

(-b+y)/(2.0*a),(-b-y)(2.0*a);;

^^

stdin(3,1): warning FS0058: possible incorrect indentation: this token is offside of context started at position (1:1). Try indenting this token further or using standard formatting conventions

(-b+y)/(2.0*a),(-b-y)(2.0*a);;

------------------^^

stdin(3,19): error FS0043: The type 'float -> 'a' does not match the type 'float'.

The Quadric Solutions code I took it from The Book F# for Scientists.

What is wrong?

Many Thanks

Hernan