# I'm not sure about this...

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• Nov 11th 2008, 04:30 AM
Alienis Back
I'm not sure about this...
Can someone check this for me, please.
• Nov 11th 2008, 04:34 AM
mr fantastic
Quote:

Originally Posted by Alienis Back
Can someone check this for me, please.

Stop at the middle line. The last line is wrong (as you would readily see if you expanded)
• Nov 11th 2008, 05:21 AM
Alienis Back
Why? Isn't the second line a perfect square trinomial?
• Nov 11th 2008, 05:27 AM
mr fantastic
Quote:

Originally Posted by Alienis Back
Why? Isn't the second line a perfect square trinomial?

I hope that when you expanded $(3a - 3b)^2$ (as I suggested) you got $9a^2 - 18ab + 9b^2$ ....

This is obviously not the same as $3a^2 - 4ab + 3b^2$.
• Nov 11th 2008, 05:28 AM
2976math
Quote:

Originally Posted by Alienis Back
Why? Isn't the second line a perfect square trinomial?

===============================================
Alienis Back,
2nd line is not correct.
see my attachment.
• Nov 11th 2008, 05:36 AM
Alienis Back
Ok. Last line is certainly wrong. No doubt. So, It shouldn't be further factor-able, should it? And where is your attachement, 2976math?
• Nov 11th 2008, 05:40 AM
2976math
Attachment 8652
Here we go.
• Nov 11th 2008, 05:42 AM
Alienis Back
2976math, look for the clip.(Wink)
• Nov 11th 2008, 05:44 AM
mr fantastic
Quote:

Originally Posted by 2976math
Attachment 8652
Here we go.

Your answer is useful in that it clearly shows why the trinomial in brackets cannot be factorised (because it's a sum of two squares). But it's not what I'd give as an answer to the original question (I'd stop at the middle line).
• Nov 11th 2008, 05:44 AM
2976math
Quote:

Originally Posted by Alienis Back
2976math, look for the clip.(Wink)

Can you see attachment?
• Nov 11th 2008, 05:51 AM
2976math
Attachment 8654

I did in hurry.
18(a^2)(b^2) should be always there from 3rd line to 5th line.
• Nov 11th 2008, 05:58 AM
Alienis Back
Yep!

2976math, That was quite useful, but is a lot more that I expected. Quite useful but as I see it, it doesn't mean my aproach is wrong. I'll keep on studying yours anyway.

Thanks a lot guys.