Solving a Quadratic Expression: How to Solve 2x^2+9x = -5

In summary, the given equation 2x^2+9x = -5 cannot be solved using traditional methods such as factoring or quadratic formula. The equation needs to be in standard form ax^2+bx+c=0 in order to use the quadratic formula. The quadratic formula is a generalized solution for equations of this form. It is recommended to seek help in the math-homework section of forums for purely math problems.
  • #1
Trent21
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2x^2+9x = -5

Solved, you can banish this thread now mods.




2x^2+9x = -5
With the given answers, nothing I can come up with matches it. I can't solve it like a normal quadratic, as it gives me no answer that matches those. And I can't factor it. Nothing that adds up to 9, that when you also multiply them, you get -5.

Divide off the 2...?
Divide off the 9.
Now I've got X + X or X^2 on the left side, and that's already not a answer match, can't solve it for X.
Cant factor it.

Square rooting it just gives The suare root of 5 divided by something, that's not a answer. So I am done, not including I feel pretty dumb not being able to solve this basic math but I am doing Thermodynamics at the moment. I can't remember what to do with this...

Only thing I heard of was to get it in standard form or something. Nothing I learned. Its this little problem that I can't figure out...

Could someone explain how to solve this, according to the answers given, and why it works? I asked others, even other friends but even they don't know, even asked a Cop at the store the other day and he didn't know. And I can't find any questions exactly like this online, is this question that tedious? Its not even difficult I bet.

Thanks
 
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  • #2
The "standard form" you spoke of is [itex]ax^2+bx+c=0[/itex] (you just get all the terms on to one side)

The reason you would want to do this is so you can use the quadratic equation. (If you don't remember the quadratic equation, it should be very easy to look up.)

As to why the quadratic equation works? It is just a generalized solution for an equation of this form (I don't want to derive it for you, but, if you're curious, that should also be easy to look up)



P.S.
In the future, the math-homework section of these forums will probably give you more help on purely math problems.
 
  • #3
Nathanael said:
The "standard form" you spoke of is [itex]ax^2+bx+c=0[/itex] (you just get all the terms on to one side)

The reason you would want to do this is so you can use the quadratic equation. (If you don't remember the quadratic equation, it should be very easy to look up.)

As to why the quadratic equation works? It is just a generalized solution for an equation of this form (I don't want to derive it for you, but, if you're curious, that should also be easy to look up)



P.S.
In the future, the math-homework section of these forums will probably give you more help on purely math problems.

Ooooooooooh hahaha, I feel pretty dumb I forgot all about the quadratic formula. I just plugged all this right in after putting it in standard form and that did the trick.

Im all good now. I am going to edit my post away so I don't embarass myself even further, thanks Nathan. : D
 
  • #4
Trent21 said:
Ooooooooooh hahaha, I feel pretty dumb I forgot all about the quadratic formula. I just plugged all this right in after putting it in standard form and that did the trick.

Im all good now. I am going to edit my post away so I don't embarass myself even further, thanks Nathan. : D

Welcome to the PF.

It is against the PF Rules to edit your OP after you have solved the problem. Please leave it as-is in the future.
 
  • #5
I restored the post, helpers please remember to first quote the OP before responding, thanks!
 

FAQ: Solving a Quadratic Expression: How to Solve 2x^2+9x = -5

What is a quadratic expression?

A quadratic expression is a mathematical expression that contains at least one squared variable. It can be written in the form of ax^2 + bx + c, where a, b, and c are constants and x is the variable.

What is the difference between a quadratic equation and a quadratic expression?

A quadratic equation is an expression that is set equal to zero, while a quadratic expression is simply a mathematical expression. However, a quadratic equation can be solved by finding the roots, or solutions, of the expression.

How do I solve a quadratic expression?

To solve a quadratic expression, you can use the quadratic formula or factoring. The quadratic formula is (-b ± √(b^2 - 4ac)) / 2a, where a, b, and c are the coefficients of the expression. Factoring involves finding two numbers that multiply to a constant term and add to the coefficient of the linear term.

What is the discriminant of a quadratic expression?

The discriminant of a quadratic expression is the part inside the square root of the quadratic formula, which is b^2 - 4ac. It can be used to determine the number of solutions of a quadratic equation. If the discriminant is positive, there will be two real solutions. If it is zero, there will be one real solution. If it is negative, there will be no real solutions.

How are quadratic expressions used in real life?

Quadratic expressions are used in many real-life situations, such as calculating the trajectory of a projectile, determining the maximum or minimum value of a function, and solving optimization problems. They are also used in engineering, physics, and economics to model and analyze various phenomena.

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