standard_description: Prove that, given a system of two equations in two variables, replacing one equation by the sum of that equation and a multiple of the other produces a system with the same solutions.
problem_activity: What is the minimum value taken by the expression
$${{{(x-}}4)^2+6}$$
? How does the structure of the expression help to see why?
Rewrite the quadratic expression
$${ x^2-6x-3}$$
in the form
$${{(x-}}$$
_____
$${{ )^2+}}$$
______ .
Rewrite the quadratic expression
$${-2x^2+4x+3}$$
in the form  ____
$${{(x-}}$$
_____
$${{ )^2+}}$$
______ .


aligns: no