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

[Amaz1ng]

But seriously, why am I getting the wrong answer here:

$$4x^2+10x= 5$$

$$4x^2+10x - 5 = 0$$

$$x=\frac{-10+\sqrt{180}}{8}$$
Answers Incorrect:

3.461 and -23

 

[Pengwuino]

Try it again. Your setup is right (although remember that + can also be a -)

 

[Amaz1ng]

My friend, I have no clue why I'm getting the wrong answers.

I was under the impression that you just plug the numbers in and it outputs correct answers.

 

[Pengwuino]

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.

 

[AlephZero]

My calculator says

$$-10 + \sqrt{180} = 3.416$$

So, you have two problems:
1. 3.461 is a typo
2. you forgot to divide by 8.

 

[S_Happens]

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.

 

[MACHO-WIMP]

I got .4271 and -2.9271

 

[Xitami]

www.wolframalpha.com

 

[Studiot]

$$\frac{{ - 10 \pm \sqrt {180} }}{8} = - \frac{{10}}{8} \pm \sqrt {\frac{{180}}{{64}}} = - 1.25 \pm \sqrt {2.8125} = - 1.25 \pm 1.677$$