F.4 MATHS(quadratic functions)

Consider the equation x^2 +(3+m)x+3m－1=0，where m is aconstant.when the
discriminant of the equation is at the minimum，find the value of m.
Sol
D=(3+m)^2－4*1*(3m－1)
=(m^2+6m+9)－(12m－4)
=m^2－6m+13
=(m－3)^2+4
m－3=0
m=3