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Thu 29/11/01 at 23:31
Regular
Posts: 787
I just had to prove that the derivative of the formula for solving quadratic equations was as follows:

========

We know that (x + m) squared = n
where n is greater or equal to 0

has the following solutions:

x = -m +/- sqrt n

So multiply (x + m) squared to give

x sqrd +2mx + m sqrd = n

or

x sqrd + 2mx + (m sqrd - n) = 0

a(x sqrd) + bx + c = 0 can be written as

x sqrd = (b/a)x + (c/a)x = 0

Therefore

2m = b/a and m sqrd - n = c/a

Therefore

m = b/(2a) and n = m sqrd - c/a

Therefore

n = (b/(2a)) sqrd - c/a

n = (b sqrd)/(4(a sqrd)) - c/a

n = ((b sqrd) - (4ac))/(4(a sqrd))

========

Does it look right to you?
Fri 30/11/01 at 00:37
Regular
"smile, it's free"
Posts: 6,460
I use the following technique to derive the quadratic formula:

1) Write out the final formula
2) Rearrange it step by step until it's a quadratic equation
3) Write out all the steps you have just done, in reverse order.

An there you go, you've derived the quadratic formula from a simple ax^2 + bx + c
Thu 29/11/01 at 23:52
Posts: 0
I dunno if this is what you're talking about, or if this is the same thing in a different form (but it doesnt look like it), but I was taught that the formula for quadratic equations is:

-B +/-(square root Bsqrd-4AC)over 2A

Im confused!
Thu 29/11/01 at 23:44
Regular
Posts: 18,185
((b sqrd) - (4ac))/(4(a sqrd))

look at that, see the problem u need to times everything out side the bracket with everything in so the sue of the brackets around the 4 is a complete wast of time the divide makes an automatic braket anyway.
Thu 29/11/01 at 23:31
Regular
"Copyright: FM Inc."
Posts: 10,338
I just had to prove that the derivative of the formula for solving quadratic equations was as follows:

========

We know that (x + m) squared = n
where n is greater or equal to 0

has the following solutions:

x = -m +/- sqrt n

So multiply (x + m) squared to give

x sqrd +2mx + m sqrd = n

or

x sqrd + 2mx + (m sqrd - n) = 0

a(x sqrd) + bx + c = 0 can be written as

x sqrd = (b/a)x + (c/a)x = 0

Therefore

2m = b/a and m sqrd - n = c/a

Therefore

m = b/(2a) and n = m sqrd - c/a

Therefore

n = (b/(2a)) sqrd - c/a

n = (b sqrd)/(4(a sqrd)) - c/a

n = ((b sqrd) - (4ac))/(4(a sqrd))

========

Does it look right to you?

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