#Example 4, page no 6
var('t')
#k is a definite physical constant. Can be anything.
k = 1
y = function('y', t)
f(t) = desolve(diff(y, t) - k*y, y)
show(f(t).subs(c=2))

plot(f(t).subs(c=2), (t, 0, 10))