Solving a Cubic Equation: How to Find the Real Root

  • Thread starter xzibition8612
  • Start date
  • Tags
    Root
In summary, the problem is to find the value of t in the equation 2t^3-4t-5=0. The quadratic formula is not applicable in this case since it is a cubic equation, but there are other methods such as the rational root theorem that can be used. However, the given solution of sqrt(2/3) may not be correct.
  • #1
xzibition8612
142
0

Homework Statement



2t^3-4t-5=0
Find t

Homework Equations



[-b-sqrt(b^2-4ac)]/2a

The Attempt at a Solution



The answer is sqrt(2/3). No idea how this came about. I tried plugging in the equation and got it wrong. :( Please help I've been struggling over this for 5 hours.
 
Physics news on Phys.org
  • #2
The quadratic formula

[tex]x=\frac{-b\pm \sqrt{b^2-4ac}}{2a}[/tex]

Is only for quadratics. That is, equations of the form

[tex]y=ax^2+bx+c[/tex]

But what you have is a cubic, so you can't use the quadratic formula. The cubic formula is way too complicated though, so we have other methods of going about solving them, such as the rational root theorem.

But now that I look at it, are you sure you wrote the cubic down correctly? The real root definitely isn't [itex]\sqrt{2/3}[/itex].
 

FAQ: Solving a Cubic Equation: How to Find the Real Root

How do I solve the equation 2t^3-4t-5=0?

To solve this equation, we need to use the factoring method. First, we need to factor out the greatest common factor, which in this case is 2. This leaves us with 2(t^3-2t-2.5)=0. Next, we can use the grouping method to factor out t from the remaining terms, giving us t(t^2-2)=2. Finally, we can factor the remaining quadratic equation using the quadratic formula or by completing the square.

What are the possible solutions to this equation?

The equation 2t^3-4t-5=0 has three possible solutions, known as roots, since it is a cubic equation. These solutions can be real, imaginary, or complex numbers.

Can I use the quadratic formula to solve this equation?

No, the quadratic formula can only be used to solve quadratic equations, which have the form ax^2+bx+c=0. The equation 2t^3-4t-5=0 is a cubic equation, so we need to use the factoring method to solve it.

Is it possible to solve this equation without factoring?

Yes, it is possible to solve this equation without factoring, but it requires more advanced methods such as using numerical methods or computer software. However, for simple equations like this one, factoring is the most efficient method.

How can I check if my solution is correct?

You can check if your solution is correct by substituting the value of t into the original equation and seeing if it satisfies the equation. For example, if your solution is t=1, then substitute 1 for t in the equation 2t^3-4t-5=0. If the resulting statement is true, then your solution is correct.

Similar threads

Back
Top