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What is the condition for the cubic equation ax^3 +bx^2 +cx+d = 0 to have real roots? (not Graphically but in terms of the coefficients a,b,c,d, ie., like we have for a quadratic eqn. that D>0)

What is the condition for the cubic equation ax^3 +bx^2 +cx+d = 0


to have real roots? (not Graphically but in terms of the coefficients a,b,c,d, ie., like we have for a quadratic eqn. that D>0) 

Grade:upto college level

1 Answers

Pratik Tibrewal
askIITians Faculty 37 Points
10 years ago
as such there is no single condition which we can use to solve the cubic.
But we can approach it in some algebraic steps:
1. differentiate, and the quadratic obtained should have D>0
2. Let's say the two roots of the quadratic obtained above is x1,x2.

Then if P(x1). P(x2) < = 0 then it has 3 real roots.

Thanks and Regards,
Pratik Tibrewal,
askiitians faculty,
BTech IITG

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