Math quadratic equation

[c0d0ps]

Not quite sure what you're insinuating there

Your "spoiler" thingy was funny because the person above you was friendly

[Toxic Tom]

Your "spoiler" thingy was funny because the person above you was friendly

 

I can be friendly and offensive

[c0d0ps]

I can be friendly and offensive

Well, everyone can be like that.

 

I prefer to be friendly, I am too lazy to be fighting (often) ^^

[martian_hunter]

x^2 - x - 20

Second degree polynominal equation are easy. What you need to do is focus on the constant first. In this case it is

-20. Now think of two the factors of -20 whose sum is -1 (because your middle term is -x. If it had been -2x you would have thought of factors with a sum of -2).

And you find out that -5x4 = -20 and -5+4=-1. Perfect.

Just put these numbers in this placeholder equation :

(x + N1)(x + N2) = 0

Where N1 & N2 are the numbers you just found out (along with the signs appropriate to the equation at hand)

and voila, you have solved it!

So,

(x - 5)(x + 4) = 0

Which gives

x = 5, x = - 4

Practice this more and you'll be able to solve such equation within 5 seconds in your head.

PS: This method won't always work. With practice you'll come to know when to use this method just by glancing at the equation.

[TideRower]

The formula I've been taught is: x= - p/2 +- sqrt (p/2)^2 - q

I am not entirely sure if it's the same are you're talking about but it looks pretty similar.

They are the same.

Your formula gives you the solution for  x²+px + q = 0

to solve x²- x - 20 = 0 you set p=-1 and q=-20

using your formula we get :

1/2 +- sqrt(81/4) = 5 or 4

[c0d0ps]

They are the same.

Your formula gives you the solution for  x²+px + q = 0

to solve x²- x - 20 = 0 you set p=-1 and q=-20

using your formula we get :

1/2 +- sqrt(81/4) = 5 or 4

Using this formula I get x1= -4 and x2= 5 and x=0,5 +- 4.5

Since it's been a while my math teacher has already helped me and instead of 81/4 it just becomes sqrt of 0.5^2+20 aka sqrt of 0,25+20

 

And no it's not the same. PQ formula as we use require x^2  while quadratic formula can be done with whatever variable/number times x^2.

[TideRower]

Using this formula I get x1= -4 and x2= 5 and x=0,5 +- 4.5

Since it's been a while my math teacher has already helped me and instead of 81/4 it just becomes sqrt of 0.5^2+20 aka sqrt of 0,25+20

 

And no it's not the same. PQ formula as we use require x^2  while quadratic formula can be done with whatever variable/number times x^2.

Well, you can rewrite your equation and use the PQ formula all the times e.g.

3x² + 2x -4 = 0 to

x² + 2/3x- 4/3 = 0 

so that you can use the PQ formula instead. Also the general formulas is the PQ formula if you set a=1.

[c0d0ps]

Well, you can rewrite your equation and use the PQ formula all the times e.g.

3x² + 2x -4 = 0 to

x² + 2/3x- 4/3 = 0 

so that you can use the PQ formula instead. Also the general formulas is the PQ formula if you set a=1.

Yes I can use the PQ formula in every/almost every second grade equation.

[mathdad]

The equation is equivalent to x*(x-1)=20. Easy now to see x=5

[ZacDaMan72]

It factors to (x-5) (x+4) so the solutions are 5 and -4.

[IMPERIUS]

a=1 because there is nothing in front of the X^2 which is the same as 1X^2

b=1 because there is nothing in front of the other X which is the same as 1X

c=-20 because it ends in -20

Then just put them into quadratic formula

Do this ^

Write down a (number in front of the first x, if its negative add the minus, if there is none write 1), b (number in front of the second x, see a) and c

Put all the numbers in that formula above and solve it

[-TesseracT-]

x^2 - x - 20 = 0

x = -(-1/2) +- sqrt((-1/2)^2 + 20)

x = 0,5 +- sqrt(0,25 + 20)

x = 0,5 +- sqrt(20,25)

x = 0,5 +- 4,5

 

x(1) = 5

x(2) = -4

 

@c0d0ps

pq-formeln är bättre än den andra skiten alla föreslår.

[c0d0ps]

x^2 - x - 20 = 0

x = -(-1/2) +- sqrt((-1/2)^2 + 20)

x = 0,5 +- sqrt(0,25 + 20)

x = 0,5 +- sqrt(20,25)

x = 0,5 +- 4,5

 

x(1) = 5

x(2) = -4

 

@c0d0ps

pq-formeln är bättre än den andra skiten alla föreslår.

Tycker jag med, fattar inte varför de hellre vill att jag ska använda "Quadratic equation formula" istället för PQ när det är PQ som jag tränar med och de gör samma sak.

[-TesseracT-]

No idea, I used to be able to do basic equasions years ago at school but I have nothing on that, maybe I'm stupid

Very useful contribution to the thread I must say. I rate 12/10.

[FireFox]

Very useful contribution to the thread I must say. I rate 12/10.

 

Yup, just as useful as this post and your post that I've just quoted 9/10

[Delusional Phil]

@c0d0ps : this is basic math ... Don't worry , in older grades you will be using a calculator to solve this in 5 seconds ...

[AlexStriz]

Oh my god how I wish I still did this kind of math. After AP Calc, math gets way too hard for me

[c0d0ps]

@c0d0ps : this is basic math ... Don't worry , in older grades you will be using a calculator to solve this in 5 seconds ...

Well, that this is "basic math" won't help me solve it.

In older grades I will know this, now I don't.

[c0d0ps]

Oh my god how I wish I still did this kind of math. After AP Calc, math gets way too hard for me

Hard is hard, it doesn't matter what you do.

Riding a bike is a simple thing but requires practice so is math (but slightly harder).

This is hard for me and ap calc is hard for you, there is not a huge difference.

 

Summarize:

Hard is hard and looking back does nothing