# How do you know if a cubic polynomial has real roots?

## How do you know if a cubic polynomial has real roots?

The roots are both real if and only if b2>c. In addition, both roots are positive if and only if b>0 and b>√b2−c (which implies c>0). Therefore we have two positive roots if and only if b>0 and b2>c>0, as before.

**What are the roots of a cubic polynomial?**

Roots of Cubic Polynomials Let us say p,q, and r are 3 roots for the equation ax3 + bx2 + cx + d. The formulas are: p + q + r = – b/a. pq + qr + rp = c/a.

**Why does a cubic polynomial always have a real root?**

This is called the complex conjugate root theorem. This means that a polynomial with real coefficients and odd degree will always have at least one real root, which answers the case for cubics. A quadratic with negative discriminant on the other hand has two, conjugate complex roots.

### How do you tell if a cubic has three real roots?

If the curve is to have three distinct roots, then the y-values of the stationary points must have opposite signs. OR −2a3+b<0and2a3+b>0,which gives−2a3

**Can a cubic have no real roots?**

You can have a cubic equation with no real roots, but it must have complex coefficients.

**What are real roots?**

The real roots are expressed as real numbers. Suppose ax2 + bx + c = 0 is a quadratic equation and D = b2 – 4ac is the discriminant of the equation such that: If D = 0, then the roots of the equation are real and equal numbers. If D > 0, then the roots are real and unequal.

#### How do you find the real roots of a function?

To find the real roots of a function, find where the function intersects the x-axis. To find where the function intersects the x-axis, set f(x)=0 and solve the equation for x.

**Which is a possible number of real roots for a cubic function?**

three

Just as a quadratic equation may have two real roots, so a cubic equation has possibly three. But unlike a quadratic equation which may have no real solution, a cubic equation always has at least one real root.

**Can a cubic polynomial have no real roots?**

Just as a quadratic equation may have two real roots, so a cubic equation has possibly three. But unlike a quadratic equation which may have no real solution, a cubic equation always has at least one real root.

## Why cubic equation has at least one real root?

If one of them is zero, two of the three roots are equal. If both of them are zero, all three roots are equal. If the maximum and minimum are of the same sign, the cubic has one real and two unreal complex roots. X*X*X=1 It is a cubic equation that has 3 roots but only one root that satisfies the equation, i.e. 1.

**Do all cubic equations have real roots?**

are all cubic equations. Just as a quadratic equation may have two real roots, so a cubic equation has possibly three. But unlike a quadratic equation which may have no real solution, a cubic equation always has at least one real root.

**What is a real root of a polynomial?**

The real number x=a is a root of the polynomial f(x) if and only if. When we see a graph of a polynomial, real roots are x-intercepts of the graph of f(x). Let’s look at an example: The graph of the polynomial above intersects the x-axis at (or close to) x=-2, at (or close to) x=0 and at (or close to) x=1.

### What is the condition for real roots?

When a, b, c are real numbers, a 0: If = b² -4 a c = 0, then roots are equal (and real). If = b² -4 a c > 0, then roots are real and unequal.

**What are real roots of a polynomial equation?**

The roots that are found when the graph meets with the x-axis are called real roots; you can see them and deal with them as real numbers in the real world.

**Do cubic functions have 3 distinct real roots?**

A cubic polynomial f has three distinct, real roots iff Δ(f)>0. The above definition of Δ is not immediately practical, since explicit formulas for the roots of a general cubic polynomial are unwieldy.

#### Which is a cubic polynomial?

Polynomials where the largest exponent on the variable is three (3) are known as cubics. Therefore a cubic polynomial is a polynomial of degree equal to 3.

**How do you find all real roots of a polynomial?**

You can find the roots, or solutions, of the polynomial equation P(x) = 0 by setting each factor equal to 0 and solving for x. Solve the polynomial equation by factoring. Set each factor equal to 0.