I found an easy-to-understand definition of accredited homeschooling on Wikipedia: Accreditation is a type of quality assurance process under which a facility's or institution's services and operations are examined by a third-party accrediting agency to determine if applicable standards are met.
Sections: Introduction, Finding information from the equation, Finding the equation from information, Word Problems. An ellipse, informally, is an oval or a squished circle. In primitive geometrical terms, an ellipse is the figure you can draw in the sand by the following process: Push two sticks into the sand. Take a piece of string and form a loop that is big enough to go around the two sticks and still have some slack.
In the present case, the method Ellipse.stretchX alters the length of one of its axes in place. If Circle inherits from Ellipse, it must also have a method stretchX, but the result of this method would be to change a circle into something which is no longer a circle. The Circle class cannot simultaneously satisfy its own invariant and the behavioural requirements of the Ellipse.stretchX method.