Have you ever owned one of those Magic 8 Balls? they look prefer comically oversized swimming pool balls, however have a flat home window built into them, so that you can see what"s insidea 20-sided die floating in venomous opaque blue goo. Supposedly, the billiard ball has actually prognostic powers; every you have to do is ask the a question, provide it a shake, and also slowly, mystically, like a petroleum-covered seal arising from an oil spill, the die will increase to the small window and also reveal the prize to your question.

You are watching: Determine the number and type of solutions

The quadratic equation consists of a Magic 8 sphere of sorts. The expression b2 - 4ac from beneath the radical authorize is referred to as the discriminant, and also it have the right to actually recognize for friend how countless solutions a offered quadratic equation has, if you don"t feel favor actually calculating them. Considering that an unfactorable quadratic equation needs a the majority of work to solve (tons of arithmetic abounds in the quadratic formula, and a entirety bunch of measures are forced in the completing the square method), it"s often useful to gaze into the mystic past to make certain the equation also has any real number solutions before you spend any kind of time actually trying to discover them.


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The discriminant is the expression b2 - 4ac, i m sorry is defined for any type of quadratic equation ax2 + bx + c = 0. Based upon the authorize of the expression, you deserve to determine how numerous real number services the quadratic equation has.


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

If you acquire a confident number, the quadratic will have two unique solutions.If you obtain 0, the quadratic will certainly have specifically one solution, a dual root.

The discriminant isn"t magic. It simply shows how essential that radical is in the quadratic formula. If the radicand is 0, because that example, then you"ll get

a single solution. If, however, b2 - 4ac is negative, then you"ll have a negative inside a square root sign in the quadratic formula, an interpretation only imagine solutions.

Example 4: without calculating them, determine how countless real services the equation 3x2 - 2x = -1 has.

Solution: set the quadratic equation same to 0 by adding 1 come both sides.

3x2 - 2x + 1= 0
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Problem 4: there is no calculating them, recognize how many real solutions the equation 25x2 - 40x + 16 = 0 has.


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

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

Because the discriminant is negative, the quadratic equation has no actual number solutions, only two imaginary ones.

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Excerpted from The complete Idiot"s guide to Algebra 2004 through W. Michael Kelley. All civil liberties reserved including the best of reproduction in entirety or in component in any form. Offered by arrangement with Alpha Books, a member of Penguin group (USA) Inc.