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# factorising

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Hw do u factorise this ..its in decimals?? x^2+1.6-4.2=0 ??

(x,  ) (x,  )

TassyG  Jan 11, 2015
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x^2+1.6-4.2=0

Is it meant to be 1.6x  Tassy?

Melody  Jan 11, 2015
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oh yh lol haha

TassyG  Jan 11, 2015
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should it be 1.6x  ?

I'll assume it should

x^2+1.6x-4.2=0

How about times both sides by 10 and see if that helps.

\$\$10x^2+16x-42=0\$\$

I think I will divide everthing by 2

\$\$5x^2+8x-21=0\$\$

I am looking for 2 numbers that multiply to -5*21 that is -105 and add to 8

Since the multply to a negative, one is neg and the other is pos.

Since they add to a positive, the bigger one will be the positive one.

some of The factors of 105 are  5,7,3,      and 15-7=8

So the numbers are  +15 and -7

Now i am going to replace 8x with 15x-7x

\$\$5x^2+15x-7x-21=0\$\$

Now factorise in pairs

\$\$\\5x(x+3)-7(x+3)=0\\
(5x-7)(x+3)=0\$\$

So either   5x-7=0    or       x+3=0

so              5x   =7     or       x=-3

so                 x=7/5     or      x=-3

do you know how to finish it?

It would have been easier just to use the quadratic formula with the original equation LOL   :)

I thought you were suppose to do it by factorising - that is why I did it this 'hard' way.

Melody  Jan 11, 2015
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it was a simultaneous equation with a quadratic and yh it is an 1.6x lol

TassyG  Jan 11, 2015
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So, are you happy with my answer ?

Melody  Jan 11, 2015
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yup obvs haha thanks

TassyG  Jan 11, 2015
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Ok I finished my earlier post.    :)

Melody  Jan 11, 2015
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I just remebered after ages that my own teacher taught me how to this equation the way you showed me but i think i forgot im really clumsy and forgetful which isnt good i must start eating more almonds and thank you again xxx

TassyG  Oct 17, 2015