Why is the quadratic formula giving me the wrong answers for 4x^2+10x=5?

In summary, the conversation is about a person getting the wrong answers for a math problem and trying to figure out why. They realize that they forgot to divide by 8 and their calculator was also giving them incorrect answers. Finally, they use all the operations listed and get the correct answers of -2.9271 and 0.4271.
  • #1
Amaz1ng
42
0
But seriously, why am I getting the wrong answer here:

[tex]
4x^2+10x= 5
[/tex]

[tex]4x^2+10x - 5 = 0[/tex]

[tex] x=\frac{-10+\sqrt{180}}{8}[/tex]
Answers Incorrect:

3.461 and -23
 
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  • #2
Try it again. Your setup is right (although remember that + can also be a -)
 
  • #3
My friend, I have no clue why I'm getting the wrong answers. o_O

I was under the impression that you just plug the numbers in and it outputs correct answers.
 
  • #4
Learn how to use your calculator :P

I mean think about it, the square root of 180 is about 13, so the numerator ~13 - 10, which is about 3, then you're going to divide by 8. So neither of your answers make sense obviously.
 
  • #5
My calculator says

[tex]-10 + \sqrt{180} = 3.416[/tex]

So, you have two problems:
1. 3.461 is a typo
2. you forgot to divide by 8.
 
  • #6
If you use ALL of the operations you listed, then you'll get the correct answers.

You're off by a factor of about 8. :smile:
 
  • #7
I got .4271 and -2.9271
 
  • #9
[tex]\frac{{ - 10 \pm \sqrt {180} }}{8} = - \frac{{10}}{8} \pm \sqrt {\frac{{180}}{{64}}} = - 1.25 \pm \sqrt {2.8125} = - 1.25 \pm 1.677[/tex]
 

1. What is a flaw in the quadratic formula?

The flaw in the quadratic formula is that it can sometimes give inaccurate solutions when dealing with very large or very small numbers. This is due to the limited precision of the quadratic formula and the possibility of rounding errors.

2. How does the flaw in the quadratic formula affect my calculations?

If you are working with numbers that are significantly larger or smaller than 1, the quadratic formula may give you solutions that are slightly off from the actual values. This can lead to errors in your calculations, especially if you are using the solutions as inputs for further equations.

3. Is there a way to avoid the flaw in the quadratic formula?

One way to avoid the flaw in the quadratic formula is to use alternative methods for solving quadratic equations, such as factoring or completing the square. These methods may be more time-consuming, but they can provide more accurate solutions.

4. Can the flaw in the quadratic formula be fixed?

The quadratic formula itself cannot be fixed, as it is a mathematical formula with inherent limitations. However, there are ways to minimize the impact of the flaw, such as using more precise calculators or software, or increasing the number of significant figures in your calculations.

5. Are there any real-world consequences of the flaw in the quadratic formula?

In most cases, the flaw in the quadratic formula will not have significant consequences in real-world applications. However, in fields such as engineering or finance where precise calculations are crucial, the potential for error introduced by the flaw may need to be considered and addressed through the use of alternative methods or more precise tools.

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