math problem

[iAsuno]

so i made this equation

x³+11x²+28x = 1872

 

x = 9

 

the problem is i can't show the whole process of getting 9 well, because once i factor the cubic equation it's pretty easy to use trial and error but i need to see how i can get 9 without trial and error. i am asking because i need to show solutions for my project. now if you think i need to find the solutions for myself and i should not ask people to do my project then please tell it and report the thread to get it closed.

 

 

[Karumu]

so i made this equation

x³+11x²+28x = 1872

 

x = 9

 

the problem is i can't show the whole process of getting 9 well, because once i factor the cubic equation it's pretty easy to use trial and error but i need to see how i can get 9 without trial and error. i am asking because i need to show solutions for my project. now if you think i need to find the solutions for myself and i should not ask people to do my project then please tell it and report the thread to get it closed.

http://www.wolframalpha.com/input/?i=x3%2B11x2%2B28x+%3D+1872

[Nineshadow]

x(x^2 + 11x + 28) = 1872

x(x-7)(x-4) = 1872

 

X can't be 0, 7 and 4.

Then go on.

Factorize 1872.

[iAsuno]

http://www.wolframalpha.com/input/?i=x3%2B11x2%2B28x+%3D+1872

 

well, it requires pro to get a step by step process.....

[juretrn]

x(x^2 + 11x + 28) = 1872

x(x+7)(x+4) = 1872

X can't be 0, - 7 and - 4.

Then go on.

Factorize 1872.

Fixed

[Nineshadow]

Fixed

Oh.

I thought it was -11x.

My bad

[iAsuno]

x(x^2 + 11x + 28) = 1872

x(x-7)(x-4) = 1872

 

X can't be 0, 7 and 4.

Then go on.

Factorize 1872.

can you do it until you get 9? just tell me if i'm asking too much.

[DigitalHermit]

so i made this equation

x³+11x²+28x = 1872

 

x = 9

 

the problem is i can't show the whole process of getting 9 well, because once i factor the cubic equation it's pretty easy to use trial and error but i need to see how i can get 9 without trial and error. i am asking because i need to show solutions for my project. now if you think i need to find the solutions for myself and i should not ask people to do my project then please tell it and report the thread to get it closed.

 

x³+11x²+28x = 1872

x³+11x²+28x-1872 = 0

(x-9)(-x²-20x-208) = 0

 

^this is how you get to x-9^

 

I needed to remember a bit of my introductory college algebra there...

 

Edit: Synthetic division will make your life easier since you already know one of the factors...

[iAsuno]

x³+11x²+28x = 1872

x³+11x²+28x-1872 = 0

(x-9)(-x²-20x-208) = 0

 

^this is how you get to x-9^

 

I needed to remember a bit of my introductory college algebra there...

 

Edit: Synthetic division will make your life easier since you already know one of the factors...

 

I am in 4th year high school (last batch of old curriculum here. students after us will follow k12 if that means anything there).... dunno if this is easy for kids my age.

 

how did you use synthetic division? i know a bit of it. but what factor did you use?

[DigitalHermit]

I am in 4th year high school (last batch of old curriculum here. students after us will follow k12 if that means anything there).... dunno if this is easy for kids my age.

 

how did you use synthetic division? i know a bit of it. but what factor did you use?

 

You gave x=9 as a solution to the equation... I worked back from there...

 

x³+11x²+28x = 1872                <----- Your original equation

x³+11x²+28x-1872 = 0             <----- Move everything to the left so it equates to zero... (easier to confirm if x=9 at this stage)

                                                 <----- Synthetic division using 'x-9' as divisor (not too sure about the term, it's been 2 years since I last handled math)

(x-9)(-x²-20x-208) = 0               <----- The other factor (aside from 'x-9') is the quotient from synthetic division...

 

I'd post my solution scratch paper if my handwriting was half-legible...

 

But here's a quick and dirty tutorial instead...

www.purplemath.com/modules/synthdiv.htm

 

Also, are you graduating by the end of this year or do you have two more years (thanks to K12)? (I see you're also from the Philippines...)

[iAsuno]

You gave x=9 as a solution to the equation... I worked back from there...

 

x³+11x²+28x = 1872                <----- Your original equation

x³+11x²+28x-1872 = 0             <----- Move everything to the left so it equates to zero... (easier to confirm if x=9 at this stage)

                                                 <----- Synthetic division using 'x-9' as divisor (not too sure about the term, it's been 2 years since I last handled math)

(x-9)(-x²-20x-208) = 0               <----- The other factor (aside from 'x-9') is the quotient from synthetic division...

 

I'd post my solution scratch paper if my handwriting was half-legible...

 

But here's a quick and dirty tutorial instead...

www.purplemath.com/modules/synthdiv.htm

 

Also, are you graduating by the end of this year or do you have two more years (thanks to K12)? (I see you're also from the Philippines...)

well, the thing is, we assume that we don't know that x = 9. we have to arrive to that. 

 

i will be graduating by the end of this academic school year.

[DigitalHermit]

well, the thing is, we assume that we don't know that x = 9. we have to arrive to that. 

 

i will be graduating by the end of this academic school year.

 

3 words to live by with this:

Trial and Error

 

protip: use your instinct when dealing with problems like this... (i.e. factor out 1872 to the prime factors, then choose the less-occuring factors first (this is a hit or miss))

protip: when in doubt, move to the next item and return to the harder ones once you've answered everything else

protip: when all else fails BRUTE FORCE...

 

If you're taking the UPCAT this weekend, hopefully I'll get to see you on campus at Diliman (if you're aiming for that one) when your classes start...

[iAsuno]

3 words to live by with this:

Trial and Error

 

protip: use your instinct when dealing with problems like this... (i.e. factor out 1872 to the prime factors, then choose the less-occuring factors first (this is a hit or miss))

protip: when in doubt, move to the next item and return to the harder ones once you've answered everything else

protip: when all else fails BRUTE FORCE...

 

If you're taking the UPCAT this weekend, hopefully I'll get to see you on campus at Diliman (if you're aiming for that one) when your classes start...

 

well, i could use trial and error and i always use that but this time i need to show how i got it because we need to make word problems and show the solution on a written report. but, i could just put use trial and error since it's so late and i need to make 1 more quadratic (already did 1) and 2 more linear (which is pretty easy but i need to think of situations). i will be taking the UPCAT in AA so i won't seee you there at diliman. maybe next year when i study there (hopefully)

[TideRower]

well, i could use trial and error and i always use that but this time i need to show how i got it because we need to make word problems and show the solution on a written report. but, i could just put use trial and error since it's so late and i need to make 1 more quadratic (already did 1) and 2 more linear (which is pretty easy but i need to think of situations). i will be taking the UPCAT in AA so i won't seee you. there at diliman. maybe next year when i study there (hopefully)

Just write that you've tried the divisors of 1872. Trial and error is your only way of solving this equation.

Then you can divide/factorize and get an equation of order 2 which you can solve easily with the apropriate formula.

There exists a formula for solving polynomial equation up to the order of 4, but the last two ones are too advanced in your case.

[DigitalHermit]

well, i could use trial and error and i always use that but this time i need to show how i got it because we need to make word problems and show the solution on a written report. but, i could just put use trial and error since it's so late and i need to make 1 more quadratic (already did 1) and 2 more linear (which is pretty easy but i need to think of situations). i will be taking the UPCAT in AA so i won't seee you. there at diliman. maybe next year when i study there (hopefully)

 

For quadratic equations (2nd power of x), you can have parabolic trajectory or speed/acceleration problems... Look for examples in your physics books and try to make up some equations that follow the mathematical 'format'...

 

For the linear ones, you can make up some constant velocity motion problems...

 

These things are what appear in some College Algebra (Math 11, Math 14, and Math 17 in UPD) classes...

 

Hopefully you're not yet required to do 3-variable algebraic equations yet (but you'll need them in college math)..

 

Edit: Also trial and error is the only way to do this as @TideRower said... By 'quadratic', it means that the maximum exponent of 'x' should only be 2...

 

Protips for UPCAT would be:

Wear comfortable clothing, bring food and drinks, and relieve yourself before the exam starts...

Browse the questions for up to a full minute before you start answering the exam (esp. math and science)

Speed through the questions you know, and leave those that you don't blank...

Guess only when you have at most 75% conviction that that is the answer (the test is right-.25wrong)...

[iAsuno]

For quadratic equations (2nd power of x), you can have parabolic trajectory or speed/acceleration problems... Look for examples in your physics books and try to make up some equations that follow the mathematical 'format'...

 

For the linear ones, you can make up some constant velocity motion problems...

 

These things are what appear in some College Algebra (Math 11, Math 14, and Math 17 in UPD) classes...

 

Hopefully you're not yet required to do 3-variable algebraic equations yet (but you'll need them in college math)..

 

Edit: Also trial and error is the only way to do this as @TideRower said... By 'quadratic', it means that the maximum exponent of 'x' should only be 2...

 

Protips for UPCAT would be:

Wear comfortable clothing, bring food and drinks, and relieve yourself before the exam starts...

Browse the questions for up to a full minute before you start answering the exam (esp. math and science)

Speed through the questions you know, and leave those that you don't blank...

Guess only when you have at most 75% conviction that that is the answer (the test is right-.25wrong)...

thanks for the tips.

mock exams were hard. is the upcat easier? people tell that mocks are harder.

[DigitalHermit]

thanks for the tips.

mock exams were hard. is the upcat easier? people tell that mocks are harder.

 

Depends on how well the mocks were made... If you pass the mocks, you'd usually have a higher chance of passing and if you do pass the UPCAT, you can most likely pass everywhere else...

Oh and one final tip, get enough sleep for the exam... I've seen someone sleep through parts of the alotted exam time...

[Guest Philosophy]

My kinda forum, love math looks like they helped already though