Wednesday, April 8, 2009

Quadratic Equation : Roots of equation

You could expect to get a question from quadratic equation in the TANCET test.

A quadratic equation is an equation of the form ax2 + bx + c = 0.

Each quadratic equation has 2 roots. The roots of the quadratic equation can be found out either by factorizing the equation or by using a formula.

If r1 and r2 are the roots of the quadratic equation, then
r1 = (-b + root(b2 - 4ac))/2a
r2 = (-b - root(b2 - 4ac))/2a

Here is a typical question in quadratic equation
Question
If 8 and 6 are the roots of a quadratic equation, then the equation is
(1) x2 + 14x + 48 = 0
(2) x2 - 14x + 48 = 0
(3) x2 + 14x - 48 = 0
(4) x2 - 14x - 48 = 0
(5) x2 + 48x + 14 = 0

If we are given the roots of a quadratic equation, i.e., r1 and r2, then the quadratic equation is (x - r1)(x - r2) = 0.
We know that the roots of equation are 8 and 6.
Hence, the equation is (x - 8)(x - 6) = 0
or x2 - 14x + 48 = 0

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