I really should be able to do this, but its been far too long since I had to do it and I was never that good at it so I keep making silly mistakes

what I've got is:

A = (2c + 2L)^2 - 4L^2

and then I start second guessing myself and ending up with 0=0 etc.....

i know that: (a+b)^2 = a^2 +2ab + b^2
but I forgotten how to deal with (2a + 2b)^2 [ = 4a^2 + 4b^2 + ??ab ]


cheers
-Robert

BODMAS is the Answer (Its what I was taught at school 50 years ago. It may not be modern, but its mathematically correct).

Do them in this order.
Brackets, Of, Division, Multiplication, Addition, Subtraction.

Hope that helps.



EDIT:

Hmm looks like a quadratic equasion.
There is a formula for them.

Also I think they are likely to have two answers for A and B.
But its been a long time!


[Edited on 22/3/2012 by wilkingj]

quote:

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Originally posted by mcerd1


i know that: (a+b)^2 = a^2 +2ab + b^2
but I forgotten how to deal with (2a + 2b)^2 [ = 4a^2 + 4b^2 + ??ab ]

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Square the first, square the second, multiply together and double.
(2a + 2b ) ^2 = 4a^2 + 4b^2 + 8ab
( I think )

quote:

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Originally posted by mcerd1
I really should be able to do this, but its been far too long since I had to do it and I was never that good at it so I keep making silly mistakes

what I've got is:

A = (2c + 2L)^2 - 4L^2

and then I start second guessing myself and ending up with 0=0 etc.....

i know that: (a+b)^2 = a^2 +2ab + b^2
but I forgotten how to deal with (2a + 2b)^2 [ = 4a^2 + 4b^2 + ??ab ]


cheers
-Robert

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There's too many variables for this to be a quadratic.

but...

A=(2c + 2L)^2 - (2L)^2

Difference of squares ie a^2 - b^2 = (a-b)*(a+b)
A=(2c + 2L -2L)*(2c + 2L + 2L)
A=2c(2c + 4L)
A=4c^2 + 8cL

when A=0
4c^2 = -8cL

divide through by 4c
c = -2L

that's as far as you get (I think); there is no single set of values that satisfies the equation.

cheers guys - sorted again

quote:

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Originally posted by jonrotheray
There's too many variables for this to be a quadratic.

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