Question

find the value of 9x^2+y^2+ z^2-6xy+2yz-6xz whenx=1, y=2 andz=-1

Answer 1

$9 \times {1}^{2} + {2}^{2} + 1 {}^{2} - 6 \times 1 \times 2 - 1 \times 2 \times 2 + 6 \times 1 \times 1 \\ =$
9+4+1-12-4+6

=4