The keyboard and screen intersect in just one line.
The intersection of 2 different planes is always a straight line. Imagine where the screen and the keyboard meet. It is a horizontal line from left to right as you are looking at the middle of your laptop.
X² + y = 4 and -y³ = 1x -5 are not linear equation because they contain a variable with a exponents. These types of equation are called quadratic equations.