Quadratic equations should know this

Bounty Hunter

could anyone tell me how to do quadratic equations when the x-squared term has a number before it.

i used to know this because i was in honours and used a "guide number"method but since dropped into pass wherre our teacher used a big X method which i could never get the hang of and unfortunatley i slowley forgot the honours method as i was not being thought it anymore.

i remember it was something fairly simple and it is important as it comes up in a huge amount of questions ...any help would be much appreciated

Raptor

The guide number method can be used, but it is slightly longer

E.g 2xsquared - 4x - 6 =0

The Guide Number is -12 (2 x -6) (the number in front of x squared multiplied by the number on its own)
For a negative guide number the factors must be one plus and one minus and in this case must add to -4 (the x term)

Factors
-4,3 -6,2 4,-3 6,-2

You use -6 and 2

You then rewrite the quadratic using the factors, ie
2xsquared -6x +2x -6

You then factor out the first half by taking out what ya can, in this case 2x

2x(x-3) (x-3)

You then put this on the other side, and find out what you need to make it "balance"

2x(x-3)+?(x-3)
The ? must equal 2

Therefore the factors are (2x+2)(x-3) = 0

Make sense? Hope so
You can always check by multiplying out again and see what you get

Bounty Hunter

what i learnt in pat doyles honours Maths has just come flooding back thanks you may have just helped me get a higher mark tommorowThanks

Bounty Hunter

actually one problem which im sure if explained will seem extremly obvious

Why must ?=2

disco_rob_funk

what the hell are you talking about raptor?

(2x^2) -4x-6=0

==

(x^2)-2x-3=0

just look at the damn thing to get (x-3)(x+1)=0

which is the same as your soln.

no, the 2 is trivial.

Why such a long convoluted process? There are enough of those in maths already!

RC

P.S. for not-so-easy ones, just remember the formula. it might look big, but it works every time and doesn't require any thought, just a spot of memory. like the rest of the damn leaving cert.

PHB

Because sometimes people can't see it so stop being so bloody mean about it. Some people would think using formulas is stupid as you can just read the question and see the anwser!!!!

Christ