Algebra

=    x^2 + 10x+21 = 0    this is a bowl shaped parabola because the leading coefficient ( of x^2) is positive

                                         the minimum will occur at the value of    x = -b/2a  

                                                                                                       x  =  -10 / (2*1) = -5

     Use this value of x in the equation to calculate the minumum value of the equation.......