4xy+z = 3 Find the equation of the plane which passes through O and is parallel to x+ - y + z = A

Use a system of linear equation to find the parabola y=ax2+bx+c that passes through the points (1,2), (0,1) and (2,6)

Find the equation of the line perpendicular to the line y=3 and passing through the midpoint of the segment joining 2, 4 and -6, 10.

Is the point (3,0) on the x-axis or y-axis? How do you know?