Un número dividido entre 8

Can someone explain the elimination method to me for this problem?

What is the axis of symmetry of the function f(x)=-(x+ 9)(x-21)

Find the directions in which the function increases and decreases most rapidly at upper p 0p0. then find the derivatives of the function in these directions. f(x,y)equals=x squared plus xy plus y squaredx2+xy+y2, upper p 0p0left parenthesis 1 comma negative 4 right parenthesis