SRL Archive - Mathematics

The area of a square is represented by (9z² - 12z + 4) ft². Which expression represents the perimeter of the square?

My answer was A - (3z-2) ft, but the correct answer was B - (3z+2) ft.

Why?

The answer is wrong.

This looks hard..
How do you do it? can you 'unsquare'? lol

Edit:
lol… i came up with -12z + 8

Edit:
Not that i only think the perimeter was only one-sided (funny joke), but i think the people who made the answer messed up -2*-2 when doing a reverse foil or similar method. That's my theory.

whichever one increases faster in the direction of it's limit and is not negative is the answer.. side lengths can't be negative..

iunno :S both seem right to me..

Perimeter is 4 sides.. those 0's represent only 1 side.. so times it by 4..
12z + 8 = y
12z - 8 = y

limit as x -> -inf for 12z + 8 = -inf pos slope always
limit as x -> +inf for 12z + 8 = + inf faster increase than the -8 counter part. -8 counter part always has -slope :S

Iunno.. this seems like a troll question.. there is no answer -_-

No tricks or troll.
It's my sisters HW problem, she is 12 years old.
Simple algebra is all that's needed.

I also think she/hobbit are correct, maybe answer in book is wrong.

The correct answer is (3z-2) Proof:

(9z^2-12z+4)=(3z-2)(3z-2) (meaning (3z-2) is the length of one side of the square

(3z-2)*4=(12z-8) (because there are 4 sides to a square)

(12z-8)= (3z-2)

It's a really easy question I guess it must just be a misprint in the book or something. Get her to tell her teacher so the other kids don't get confused.

I don't know what ft means but:
sqrt(9z² - 12z + 4) = 3z-2 or -(3z-2)
sqrt(9z² - 12z + 4) = 3z-2 or -3z + 2

I believe the perimeter would be:
4 * (3z-2) = 12z-8 or 4 * (-3z+2) = -12z+8

From: masterBB
I don't know what ft means but:

ft means foot which is an imperial form of measurement.

From: YoHoJo
maybe answer in book is wrong.

Very probable, especially considering for my 3rd year graph theory course we find at least one mistake in the textbook answer key per assignment.

From: YoHoJo
Why?

simple - you know that 3z-2 is length of one side so it cannot be the correct answer unless 3z-2 = 0, which would not yield square to begin with

that leaves the answer 3z+2

and of course that means we can calculate z by saying:

4(3z-2) = 3z+2
9z = 10

so there you go - the square is 1 1/3 x 1 1/3 and length of all 4 sides is 5 1/3

no misprint… just a trick question

From: zmon

4(3z-2) = 3z+2
9z = 10

so there you go - the square is 1 1/3 x 1 1/3 and length of all 4 sides is 5 1/3

no misprint… just a trick question

i disagree with your process - clearly there is a solution for z, but that involves knowing the answer (3z+2). could there be another correct solution?


the problem seems difficult for a middle school textbook…

I agree with Hobbit, answer is wrong but big of a grave dig guys…

(3z - 2)^2 = (3z - 2)(3z - 2) = (3z)(3z) - 2(3z) - 2(3z) + (-2)(-2) = 9z^2 - 12z + 4

From: putonajonny
I agree with Hobbit, answer is wrong but big of a grave dig guys…

(3z - 2)^2 = (3z - 2)(3z - 2) = (3z)(3z) - 2(3z) - 2(3z) + (-2)(-2) = 9z^2 - 12z + 4

Yeah, but (3z - 2) is only one side of the shape. The equation asks for perimeter…

well we know the perimeter isnt 3z-2 because thats one side, and it would only work if the side was 0, then it isnt a square. the perimeter should be 12z-8 but without more info we cant know anything more about it

From: Yago
Yeah, but (3z - 2) is only one side of the shape. The equation asks for perimeter…

Yeah sorry, completely misread it, just 4 times what I said then… which isn't an option :S

From: putonajonny
Yeah sorry, completely misread it, just 4 times what I said then… which isn't an option :S

My guess is that there probably was more than two choices and A or B seemed the bests answers at the time, but we may never know…