Difficulties with parametric plots

I tried/got:


julia> f(a) = ( (1/2)*(pi*a*i/r + 2r)cos(a), 1/2(pi*a*i/r + 2r)*sin(a) )
f (generic function with 1 method)

julia> plot( f(x) )
ERROR: MethodError: no method matching +(::StepRangeLen{Float64, Base.TwicePrecision{Float64}, Base.TwicePrecision{Float64}}, ::Float64)
For element-wise addition, use broadcasting with dot syntax: array .+ scalar
...

So then I tried:

julia> using Plots; gr();
julia> i=0.2;r=25.1; x=r:i:248*pi;

julia>  f(a) = ( (1/2)*(pi*a*i/r + 2r)cos(a), 1/2(pi*a*i/r + 2r)*sin(a) )
f (generic function with 1 method)

julia> plot( f, x )

It didn’t crash, but instead gave me: