Question

A total x feet of fencing is to form 3 sides of a level rectangular yard. What is the maximum area of the yard in term of x?
A) x^2/9
B) x^2/8
C) x^2/4
D)x^2
E)2x^2
Please, help

Answer 1

oops meant to write x

Answer 2

one sec

Answer 3

\[2L+W=x \\ A=LW=L(x-2L)\]

Answer 4

So we want to find A' here

Answer 5

yes, then??

Answer 6

x is a constant I believe
\[A=Lx-2L^2 \\ A'=x-4L \\ A'=0 \implies x=4L \\ A=L(x-2L)=L(4L-2L)=L(2L)=2L^2 \\ \]
I think you can find A in terms of x now since x=4L

Answer 7

still processing?

Answer 8

Yes. Thanks a lot. I got the right answer. It is not test, just practice exam with the answer sheet. But I want to know logic.

Answer 9

Why are you doing calculus 1 problems?

Answer 10

oh, is it calculus problem??

Answer 11

Yes it is an optimization problem

Answer 12

Question: why do you link to derivative?

Answer 13

because it say to maximize

Answer 14

I assume it is an algebra problem and get no outlet

Answer 15

usually those in the cal problems I have seen they actually gave a number instead of saying x

Answer 16

I am prepare for my GRE test for maths major students. ha!!!

Answer 17

http://tutorial.math.lamar.edu/Classes/CalcI/Optimization.aspx
this example one here is pretty similar

Answer 18

My tough one is English, not math.

Answer 19

except as I said they say 500 feet instead of x feet

Answer 20

Any tips for GRE math practice?? I have only 1. :)

Answer 21

there was a question
and I think it was on the gre
it was my favorite question to
give me a sec and I will remember it

Answer 22

solve for x+y
\[x^2+y^2+2xy+2x+2y=-1 \]

Answer 23

there was a similar question on the gre or it might have been on another standard test
can't remember which standard test

Answer 24

hihihi... I have time. I will study carefully before taking the test. But you know, I am old. hahaha..... I am slow!!

Answer 25

that question isn't too bad
did you want me to show you how to do it
or did you want to try it first

Answer 26

show me, please

Answer 27

\[x^2+2xy+y^2+2x+2y+1=0 \\ (x+y)^2+2(x+y)+1=0 \\ (x+y+1)^2=0 \\ x+y+1=0 \\ x+y=-1 \]

Answer 28

I turned it into a quadratic in terms of (x+y)

Answer 29

What if we let x+y =t??

Answer 30

oh, yea, we met there

Answer 31

good luck on your gre
if i could figure out anything to tell you to help you I will
I probably should have studied for it back in the day more than I did

Answer 32

Sure. Again, thanks for the help.

Answer 33

np

Answer 34

What is the units digit in standard decimal expansion of the number 7^(25)
I don't get what it mean

Answer 35

since \(7^{25} = 1.34106862 *10^{21}\)
hence the number of digits after decimal point is 8 but it is not one of the options which are 1,3,5,7 or 9

Answer 36

@freckles

Answer 37

To this problem, if I don't have calculator, how can I find out the answer?

Answer 38

so you are trying to find out the length of the number 7^(25) ?

Answer 39

problem 14 https://www.ets.org/s/gre/pdf/practice_book_math.pdf

Answer 40

on

Answer 41

oh*

Answer 42

the units digit is the ones digit

Answer 43

answer is 1

Answer 44

total??

Answer 45

nope, answer is 7

Answer 46

wait standard notation is not scientific notation is it ?

Answer 47

I am not sure.

Answer 48

there was need to write in scientific notation
because standard notation is different from scientific notation

Answer 49

7^(25) mod 10 will give you number in 1's digit

Answer 50

or aka units digit

Answer 51

\[4^2=16 \text{; 16 is standard notation for } 4^2 \\ 4^2=1.6 \times 10 \text{ is sceinfict notation }\]

Answer 52

I missed the word no in
there was need to write in scientific notation

there was no need to write in scientific notation*

Answer 53

to this http://mathcentral.uregina.ca/QQ/database/QQ.09.06/tyrone1.html
they said that the units digit is the last digit of the number in standard form
in decimal form, the unit digit of 7^25 is the last one, which is 2, not 7 : (

Answer 54

\[7^{2} \mod 10=9 \\ 7^4 \mod 10 =9 \cdot 9 \mod 10=81 \mod 10=1 \\ 7^{4(6)+1} \mod 10=(7^4)^6(7) \mod 10=1^6(7) \mod 10 =7 \\ 7^{25} \mod 10=7 \]

Answer 55

the units digit is the first number
it is the one's digit
that is what that picture above says also

Answer 56

for example 61
do you call 1 the first digit because I do
and 6 is the last digit

1 is in the one's place (or the units place)
6 is in the ten's palce

Answer 57

oh I think I see where you are getting confused

Answer 58

\[7^{25} = 1.34106862 *10^{21} \]
you think this equality is exact when it is not

Answer 59

and even if it was exact you would say the units digit is 0
but it is not the case because this equation is not exact

Answer 60

like you still need to move that decimal to the right like 21 times

Answer 61

2 is not in the one's digit

Answer 62

http://www.wolframalpha.com/input/?i=7%5E25+

Answer 63

the number where it says result is the number in standard notation

Answer 64

oooooooooooooooooh!! got you

Answer 65

a mod 10
should always give you the units digit of a

Answer 66

modular method help me out
7^0 -----1 last digit
7^1 -----7 last digit
7^2 -----9
7^3 -----3
7^4-----1
hence the cycle is 4,
25 = 4*6 +1, hence \(7^25 = 7^24 *7 , but the last digit of 7^24 is 1 then *7 =7

Answer 67

yah

Answer 68

Thanks a ton. :) I do appreciate.

Answer 69

np

Answer 70

interesting practice exam
I think they have made changes to it seen I last took the gre
I feel like that was 8 years ago or something :p

Answer 71

I don't remember linear algebra or number theory on it

Answer 72

but maybe there was some