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Posers and Puzzles

Larkfield!(kent, uk)

Joined 19 Oct '01 Moves 14933 can someone help me here, this was in my GCSE maths paper and i didnt have a clue how to solve it..
prove that 20x + x squared = 400 (prove means u dont answer it im guessing)

Norway

Joined 19 Dec '02 Moves 483 I cannot see how you're supposed to prove that:
20x + x^2 = 400
However, it is possible to solve it, and find x (I suppose that's the purpose of this task):
20x + x^2 = 400
x^2 + 20x + 100 = 500
(x + 10)^2 = 500
x + 10 = [+/-]sqrt(500)
x = [+/-] 10sqrt(5) - 10
If you'd like, you can say:
x = 10([+/-]sqrt(5) - 1)
[+/-] -- plusminus-thingy (\pm in (La)TeX) π

maybe it was
prove that 20x squared divided by x^2 = 400

Your Blackened Sky

Joined 12 Mar '02 Moves 15128 Originally posted by astevenson
can someone help me here, this was in my GCSE maths paper and i didnt have a clue how to solve it..
prove that 20x + x squared = 400 (prove means u dont answer it im guessing) if you solve it, then you are proving it, are you not? but would that not be possible for any equation of that form? i.e. 463x+2x^2=547, albeit that x will not always be in interget...?

R.I.P.

Joined 21 Dec '01 Moves 8578 Maybe it is possible if the x was something on the lines of .9975124???? (I run out digits on my calcπ)

R.I.P.

Joined 21 Dec '01 Moves 8578 Did in excel instead x= 0.997512422417805 π

Joined 26 Apr '03 Moves 26510 Originally posted by astevenson
can someone help me here, this was in my GCSE maths paper and i didnt have a clue how to solve it..
prove that 20x + x squared = 400 (prove means u dont answer it im guessing) For the wording of that question to make sense, they must have given you the value of X or made you work it out in an earlier part of the question.