Deciding the Quadratic Method Flashcards

All 5 cards in this deck

Which method should you use when a quadratic equation asks for an exact answer in surd form, e.g. $\frac{p\pm q\sqrt{15}}{2}$?

Completing the square, or the quadratic formula left in surd form (not rounded).

True or false? Every quadratic equation can be solved by factorising.

False. Many have no integer factorisation, so use the quadratic formula or complete the square.

A quadratic equation from a length or area problem gives one positive and one negative solution. What do you do?

Reject the negative solution (a length cannot be negative) and give only the positive value.

Where on the graph of $y=x^2+3x-3$ are the solutions of $x^2+3x-3=0$ read off?

At the $x$-coordinates of the points where the curve crosses the $x$-axis.

True or false? To find approximate solutions of $x^2-2x=4$ from the graph of $y=x^2-2x$, you read off where the curve crosses the $x$-axis.

False. You read off the $x$-values where the curve meets the line $y=4$.