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/sci/ - Science & Math

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5709433 No.5709433 [Reply] [Original]

Hello /sci/

I'm teaching myself algebra, and I'm having some difficulty understanding 'completing the square'.

I think I understand the concept behind it, but I can't seem to solve this equation. If anyone could help, I'd appreciate it.

x^2-3x-5=0

The method I was using before was getting the equation into the form:

a(x+d)^2+e=0 where d = b/2a and e = c-b^2/4a

However, when I do this, I get irrational numbers...

>> No.5709450

you mean irrationals in x? or in the coeficients?

you will usually get irrationals when solving a trinomial/quadratic

>> No.5709464

>>5709450
Yeah, the problems so far have dealt with irrational numbers, I'm just not sure where I'm going wrong... I've gotten as far as:

(x-3/2)^2 but I'm not sure how to work out the rest. The book says the answer is: x=3/2 +- √29/2

I have no idea how they got √29/2

>> No.5709487

If x^2-3x-5=0 is to have the form a(x+d)^2+e=0 then the following must hold: a=1, d=-3/2, e=-29/4. This is completely obvious. What exactly is your problem?

>> No.5709497

>>5709487
Seriously though, what the fuck is your problem. Just now I understood what you're trying to do, and it's ridiculously trivial: if a(x+d)^2+e=0 then obviously x=-d +- sqrt(-e/a). It's obvious what a,d and e are, so WHAT THE FUCK IS YOUR PROBLEM?!