904.sagews

var('x,l')

(x, l)

solve(0==(x-l)+exp(-x), x)

[x == (l*e^x - 1)*e^(-x)]

var('x,l')
implicit_plot((x-l)+exp(-x),(l,-5,15),(x,-10,15))

@interact
def _(l=(-10..10)):
    (plot((x-l),(x,-3,3))+plot(exp(-x),(x,-3,3))).show()

l