Question

Find the value = 9x^2+y^2+z^2-6xy+2yz-6zx if x=1,y=2,z=-1

Answer 1

9*(1)^2+(2)^2+(-1)^2-6*1*2+2*2*(-1)-6*(-1)*1
=9+4+1-12-4+6
=20-16
=4