# Weekly maths challenge...

#### Liam W

##### Well-known member
I've added this to my signature...

Got the solution? I'm doing it in school...

#### Martok

##### Well-known member
Yep, got the solution but just in case this is one of your school problems I'd best not give you the answer.

All I will say is complex numbers, nice.

#### Liam W

##### Well-known member
I literally made it up on the spot while typing it out into the signature box

I better had complete it now, so I know if other's get it right!

#### Martok

##### Well-known member
I literally made it up on the spot while typing it out into the signature box

I better had complete it now, so I know if other's get it right!
Oh OK, I believe you.

x=i-1
or if you prefer it written 'correctly' as a complex number,
x=-1+i

#### RobParker

##### Well-known member
Oh OK, I believe you.

x=i-1
or if you prefer it written 'correctly' as a complex number,
x=-1+i
Isn't it actually x = -1 +/- i?

Liam, I assume you're doing quadratic equations at school?

Set the two expressions you've been given as being equal (as you're told in the question) and then get it into the form 0 = ax^2 + bx + c

The use the quadratic formula to get the value of x.

#### Martok

##### Well-known member
Isn't it actually x = -1 +/- i?
Yes, you are correct,
x=-1+i
and
x=-1+i

because of course sqrt of -1 is indeed either -i or +i

#### RobParker

##### Well-known member
Yes, you are correct,
x=-1+i
and
x=-1+i

because of course sqrt of -1 is indeed either -i or +i
Erm no...I actually meant because the quadratic formula is (-b +/- sqrt(b^2-4ac))/2a. You only did the + part of that.

#### Martok

##### Well-known member
Erm no...I actually meant because the quadratic formula is (-b +/- sqrt(b^2-4ac))/2a. You only did the + part of that.
Yes of course! Though (-i)^2 and i^2 both equal sqrt -1, you are correct that it is from the quadratic equation that you get both of the answers for x.

*EDIT* Actually were both correct. You just did it using the quadratic formula to calculate the answer. I did it from the quadratic equation and resolving as far as x=-1 + sqrt(-1) I just forgot that sqrt(-1) has two answers, -i and +i. What the quadratic formula reminds us of is that there are two answers to any sqrt, the positive and the negative hence ± in the formula.

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#### Chris D

##### XenForo developer
Staff member
I've given this a lot of thought and I've come to the conclusion that x = bacon.

#### Tracy Perry

##### Well-known member
I've added this to my signature...

Got the solution? I'm doing it in school...
That's easy... x = the 24th letter of the english alphabet.

#### mistypants

##### Well-known member
Oh man, I don't miss Calculus. So glad I'm almost done with my math credits.

#### Liam W

##### Well-known member
Well done all

I did this on paper last night... I forgot to change the minus to a plus on the 10 when transferring it over

Solution:

5x^2+12x = 2(x-5)

5x^2+12x = 2x-10

5x^2+12x-2x+10=0

5x^2+10x+10=0

x=-b±sqrt(b^2-4ac)/2a

x=-10±sqrt(10^2-4x5x10)/2x5

x=-10±sqrt(100-200)/10

x=-10±sqrt(-100)/10

x=-10+sqrt(-100)/10 OR x=-10-sqrt(-100)/10

x=-10+10i/10 or x=-10-10i/10

x=-1+i or x=-1-i

#### BirdOPrey5

##### Well-known member
While I liked math, can't say I miss this stuff. I can say I have never had to do a quadratic equation in the 10 years I spent as a project engineer, then director of engineering. (Or 5 years since.)

#### CTXMedia

##### Formerly CyclingTribe
I'll be honest and say I've absolutely no idea whatsoever ...