Quadratic equation

a and b are the roots of x2 + 5x + k = 0

k = products of the two roots
Hence, k = ab

=====
Proof:
a and b are the roots of x2 + 5x + k = 0
(x - a) = 0 and (x - b) = 0
(x - a)(x - b) = 0
x2 - (a + b)x + ab = 0

x2 + 5x + k = 0
x2 - (a + b)x + ab = 0

x2 + 5x + k = x2 - (a + b)x + ab
Compare the constant terms on the both sides.
k = ab
=