NEED HELP WITH WORKING OUT plzzzzzz (1 Viewer)

[Nerd Queen]

I'm trying, keyword, trying to study for the half yearlies but i am having great difficulty with a certain question. this question was in my last assesment task and has just popped up in a revision sheet i got

write the quadratic equation whose roots are 2+(root 5) and 2-(root 5)

sorry dont know how to do the square root sign on pc.

anyway in the assement i had the working for this wrong but the answer right.

what i did was i added the roots and times them to find ( alpha + beta ) or -b/a and ( alpha x beta ) or c/a

then worked out that the equation would be:

x^2-4x+1=0

which is the right answer but how am i supposed to work it out? is there a formula that i missed?

plz, i need help urgently. if anyone can help me i will owe them BIG TIME

MATHS EXAM IN 6 days ..........according to my calculations

 

[Dreamerish*~]

[x-(2+./5)][x-(2-./5)]

= x^2 - x(2-./5) - x(2+./5) + (2-./5)(2+./5)
= x^2 - 2x + x./5 - 2x - x./5 + 4 - 5
= x^2 - 4x - 1

are you sure the answer was x^2 - 4x + 1?

 

[Nerd Queen]

yes i am sure... i just figured it out anyway, found in on some website through google... the formula thing anyway .... and the answer still works out the same

the thingy i found was

( x - alpha )( x - beta ) = 0

it worked i am so relieved

thanx for trying to help

 

[Nerd Queen]

Oh i realise now that is the formula thing u had, i still got x^2 - 4x+1

here is my working

( x - 2 +./5)( x - 2 -./5) = 0
x^2 - 2x -x./5 -2x +4 +2./5 +x./5 -2./5 -5

x^2 -4x +1 = 0

 

[Trev]

Your working is wrong because you have not included the whole 'root' in brackets, or whatever. Take note of Dreamerish!...
[x-(2+./5)][x-(2-./5)] There are brackets in that question, you have excluded them so you have resulted with,
( x - 2 +./5)( x - 2 -./5) rather than;
( x - 2 -./5)( x - 2 +./5) if you take away the brackets, remember the negative sign is there!
EDIT: I am wrong, they are still the same.

 

[Nerd Queen]

yea i know and i did that in my head cuz the negative of one of the roots would have been the same as the other.

i re-did it anyway

i got all the same working but.... *nerd queen honorably accepts defeat* ... i might have (DID) made a small mistake.

i was so into beleiving that the answer i had was right ( because the teacher marked it right) that i didn't think when i was adding the last part and as a result got

4 - 5 = 1 rather than -1

thanx 4 that

*Nerd Queen hangs head in shame*

its always the stupid things like that that make me loose marks.

Thanx again

 

[Trev]

That's okay, I tend to lose marks for stupid errors and small things I overlook.
Yes, you are correct that they are both the same - so I edited my post. The humilty!

 

[Nerd Queen]

There's nothing 4 YOU to feel humiliated about. I'm the one who cant do simple addition and subtraction.

*Nerd Queen sobs quietly in corner*

But I'm NOT WORRIED (*cough*)

 

[acmilan]

There's nothing 4 YOU to feel humiliated about. I'm the one who cant do simple addition and subtraction.

*Nerd Queen sobs quietly in corner*

But I'm NOT WORRIED (*cough*)

Those errors are normal. I was still getting things like 2*3 wrong in exams leding up to the hsc. Some notable errors I made in actual exams include 2*3 = 5, a⁰ = 0, 24 - 8 = 18 and so forth

 

[Nerd Queen]

Really? its nice to know that I'm not alone in making stupid mistakes. But trust me I've

made stupider mistakes than that! I really need to learn to think carefully about what I am

doing. But there lies a danger in wasting time!

 

[acmilan]

Really? its nice to know that I'm not alone in making stupid mistakes. But trust me I've

made stupider mistakes than that! I really need to learn to think carefully about what I am

doing. But there lies a danger in wasting time!

Yes, however that was a year ago now. Those mistakes are long gone now and they will go for you the more you practice Id hate to lose marks like that in uni maths, especially since the questions in advanced maths are so damn hard already!

 

[Trev]

Those errors are normal. I was still getting things like 2*3 wrong in exams leding up to the hsc. Some notable errors I made in actual exams include 2*3 = 5, a⁰ = 0, 24 - 8 = 18 and so forth

Ah yes, i'm a lost cause when it comes to basic arithmetic.

 

[Nerd Queen]

I hope they do go away. I get really angry that I lose marks over stupid things like that. Did you do prac papers and past papers and stuff? cuz that is supposed to be a big help. I've been planning to do some things like that for a while but time is valuable right now, there just doesn't seem to be enough. Also because we haven't done every single topic yet I get put off those things very easily when it comes to a question I don't know how to do. More than anything I need to be "self-motivated", but I just can't seem to be.