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Question

Please tell me about ....DISCRIMINANT AND NATURE OF ROOTS PPZZ FAST..

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Solution

Discriminant ∆ = b2 - 4ac

Depending on the discriminant we shall discuss the following cases about the nature of roots α and β of the quadratic equation ax2 + bx + c = 0.

When a, b and c are real numbers, a ≠ 0

Case I: b2 - 4ac > 0

When a, b and c are real numbers, a ≠ 0 and discriminant is positive (i.e., b2 - 4ac > 0), then the roots α and β of the quadratic equation ax2 + bx + c = 0 are real and unequal.

Case II: b2 - 4ac = 0

When a, b and c are real numbers, a ≠ 0 and discriminant is zero (i.e., b2 - 4ac = 0), then the roots α and β of the quadratic equation ax2 + bx + c = 0 are real and equal.

Case III: b2 - 4ac < 0

When a, b and c are real numbers, a ≠ 0 and discriminant is negative (i.e., b2 - 4ac < 0), then the roots α and β of the quadratic equation ax2 + bx + c = 0 are unequal and imaginary. Here the roots α and β are a pair of the complex conjugates.

Case IV: b2 - 4ac > 0 and perfect square

When a, b and c are real numbers, a ≠ 0 and discriminant is positive and perfect square, then the roots α and β of the quadratic equation ax2 + bx + c = 0 are real, rational unequal.

Case V: b2 - 4ac > 0 and not perfect square

When a, b and c are real numbers, a ≠ 0 and discriminant is positive but not a perfect square then the roots of the quadratic equation ax2 + bx + c = 0 are real, irrational and unequal.

Here the roots α and β form a pair of irrational conjugates.

Case VI: b2 - 4ac is perfect square and a or b is irrational

When a, b and c are real numbers, a ≠ 0 and the discriminant is a perfect square but any one of a or b is irrational then the roots of the quadratic equation ax2 + bx + c = 0 are irrational.


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