This discussion is closed.
Mark
Badges:
#1
Report 18 years ago
#1
I'm really stuck on this one, any ideas?

(N+500) (1-3N)

Cheers

-----------------------------
Mark
0
Daniel25386
Badges:
#2
Report 18 years ago
#2
Multiplied out you get N-3N^2+500-1500N, which simplifies to 3N^2+1499N-500=0. Then just use the
quadratic formula N= [-b (plus or minus) sqrt(b^2-4ac)]/2a, where a b and c are 3, 1499 and -500.
You should get 1/3 and -500
0
Stan Brown
Badges:
#3
Report 18 years ago
#3
Mark <[email protected]> wrote in uk.education.maths:
[q1]>I'm really stuck on this one, any ideas?[/q1]
[q1]>[/q1]
[q1]>[/q1]
[q1]>(N+500) (1-3N)[/q1]

Multiply it out. A common mnemonic is "FOIL", meaning First, Outside, Inside, Last -- which reminds
you to multiply all possible pairs of terms. Using "FOIL" you have

N - 3N^2 + 500 -1500N

Then collect similar terms (like terms):

-3N^2 - 1499N + 500
--
Stan Brown, Oak Road Systems, Cortland County, New York, USA http://oakroadsystems.com/ "What in
heaven's name brought you to Casablanca?" "My health. I came to Casablanca for the waters." "The
waters? What waters? We're in the desert." "I was misinformed."
0
Robert Low
Badges:
#4
Report 18 years ago
#4
In article <[email protected] b-fd.aol.com>, Daniel25386 <[email protected]> wrote:
[q1]>Multiplied out you get N-3N^2+500-1500N, which simplifies to 3N^2+1499N-500=0. Then just use the[/q1]
[q1]>quadratic formula N= [-b (plus or minus) sqrt(b^2-4ac)]/2a, where a b and c are 3, 1499 and -500.[/q1]
[q1]>You should get 1/3 and -500[/q1]

I don't think he wanted to solve the equation (n+500)(3n-1)=0, but in any case, multiplying out and
using the quadratic formula has to be just about the worst possible way to get the right answer.

If (n+500)(1-3n)=0, then either n+500=0, i.e. n=-500, or 1-3n=0, i.e. n=1/3.

That said, I don't know what the original poster *did* want, since I'm hard put to make
(n+500)(1-3n) any 'simpler'.

Just to get slightly on-topic:

<peeve> The use of 'simplify' in a student exercise is a Bad Thing. Which of two equivalent
expressions is 'simpler' is impossible to say in general, and which is more useful depends on the
context. </peeve>

--
Rob. http://www.mis.coventry.ac.uk/~mtx014/
0
Robert Low
Badges:
#5
Report 18 years ago
#5
Stan Brown <[email protected]> wrote:
[q1]>Mark <[email protected]> wrote in uk.education.maths:[/q1]
[q2]>>I'm really stuck on this one, any ideas? (N+500) (1-3N)[/q2]
[q1]>Multiply it out. -3N^2 - 1499N + 500[/q1]

Personally, I think that that has complicated the expression, not simplified it.
--
Rob. http://www.mis.coventry.ac.uk/~mtx014/
0
Stan Brown
Badges:
#6
Report 18 years ago
#6
Robert Low <[email protected] ac.uk> wrote in uk.education.maths:
[q1]><peeve> The use of 'simplify' in a student exercise is a Bad Thing. Which of two equivalent[/q1]
[q1]>expressions is 'simpler' is impossible to say in general, and which is more useful depends on the[/q1]
[q1]>context. </peeve>[/q1]

Hear, hear!

Which is simpler, (x-1)^-4 or 1/(x-1)^4 ? x^4 - 4x^3 + 6x^2 - 4x + 1 or (x-1)^4 ?

I like to see clearer terms on exams, such as "multiply out" or "express as a sum or difference of
trig functions" or "simplify (no negative or fractional exponents)".

--
Stan Brown, Oak Road Systems, Cortland County, New York, USA http://oakroadsystems.com/ "What in
heaven's name brought you to Casablanca?" "My health. I came to Casablanca for the waters." "The
waters? What waters? We're in the desert." "I was misinformed."
0
Mr. Wood
Badges:
#7
Report 18 years ago
#7
[q1]>A common mnemonic is "FOIL"[/q1]

That's fine, but not as much fun as 'Grinny Gorilla' !! My pupils are trained to spot him... and
they always draw in his two eyebrows, nose and mouth to help them see which terms to multiply.

(In 'FOIL' terms it would be F, L for the eyebrows, I for the nose and O for the mouth.)

It's not very formal, but for some reason this makes expanding brackets a little more bearable - and
they seem to remember it better than FOIL, even though the process is identical!

I got 'Grinny Gorilla' from a colleague a few years back - has anyone else heard of him?

Dan.
0
X
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

If you do not get the A-level grades you want this summer, what is your likely next step?

Take autumn exams (207)
46.94%
Take exams next summer (63)
14.29%
Change uni choice through clearing (100)
22.68%
Apply to uni next year instead (45)
10.2%
I'm not applying to university (26)
5.9%

Watched Threads

View All