Have you ever before owned one of those Magic 8 Balls? They look like comically oversized pool balls, however have actually a flat home window developed into them, so that you have the right to see what"s insidea 20-sided die floating in disgusting opaque blue goo. Supposedly, the billiard ball has prognostic powers; all you need to carry out is ask it a question, offer it a shake, and also gradually, mystically, prefer a petroleum-covered seal emerging from an oil spill, the die will rise to the bit window and also expose the answer to your question.

You are watching: How can you tell when a quadratic equation has no real solutions?

The quadratic equation contains a Magic 8 Ball of sorts. The expression b2 - 4ac from beneath the radical sign is referred to as the discriminant, and it can actually identify for you how many type of solutions a given quadratic equation has actually, if you do not feel choose actually calculating them. Considering that an unfactorable quadratic equation calls for a lot of work-related to fix (lots of arithmetic abounds in the quadratic formula, and a whole bunch of procedures are required in the completing the square method), it"s frequently useful to gaze into the mystic beyond to make certain the equation also has actually any kind of genuine number options before you spfinish any type of time actually trying to uncover them.

Talk the Talk

The discriminant is the expression b2 - 4ac, which is characterized for any quadratic equation ax2 + bx + c = 0. Based upon the sign of the expression, you deserve to identify exactly how many type of real number solutions the quadratic equation has.

Here"s how the discriminant functions. Given a quadratic equation ax2 + bx + c = 0, plug the coefficients right into the expression b2 - 4ac to view what results:

If you gain a positive number, the quadratic will have actually 2 distinct solutions.If you acquire 0, the quadratic will have actually precisely one solution, a twin root.

The discriminant isn"t magic. It just shows just how crucial that radical is in the quadratic formula. If its radicand is 0, for instance, then you"ll get

a single solution. If, yet, b2 - 4ac is negative, then you"ll have actually a negative inside a square root sign in the quadratic formula, interpretation just imaginary remedies.

Example 4: Without calculating them, recognize just how many type of genuine solutions the equation 3x2 - 2x = -1 has.

Solution: Set the quadratic equation equal to 0 by including 1 to both sides.

3x2 - 2x + 1= 0
You"ve Got Problems

Problem 4: Without calculating them, recognize exactly how many kind of genuine options the equation 25x2 - 40x + 16 = 0 has actually.

Set a = 3, b = -2, and also c = 1, and also evaluate the discriminant.

b2 - 4ac=(-2)2 - 4(3)(1)= 4 - 12= -8

Since the discriminant is negative, the quadratic equation has actually no genuine number remedies, just 2 imaginary ones.

See more: How Hard Can A Horse Kick Kill You ? Can A Horse Kick Kill You


Excerpted from The Complete Idiot"s Guide to Algebra 2004 by W. Michael Kelley. All rights reserved including the ideal of remanufacturing in whole or in part in any develop. Used by plan through Alpha Books, a member of Penguin Group (USA) Inc.