factorization

ok my brain is being really slow at the moment

Find x by factorization if x2 - 13x + 36 = 0

I have forgot how to factorize, I get it once someone shows me

so could someone show me

will rep =)

Reply 1

nota bene

15

Assuming that is x^2 you have (x+a)(x+b)=x^2-13x+36 expand LHS and compare coefficients.

Spoiler

x = -9, -4

You want to find two numbers that multiply to give 36, and add up to -13.

The two numbers -4 and -9 multiply to give 36 and add up to -13.

(x-9)(x-4)=0

Reply 4

rbnphlp

11

Adonis

ok my brain is being really slow at the moment

Find x by factorization if x2 - 13x + 36 = 0

I have forgot how to factorize, I get it once someone shows me

so could someone show me

will rep =)

you need two factors that will give you the product 36 and sum -13

hint

edit :damm slow as a snail

Reply 5

miss_p

8

I think it's (x-9)(x-4)

Edit: Grrr I wasn't the first one to do it! But I'm happy because that's the first bit of maths I've done since June 2008! And seems it was correct! :biggrin:

Reply 6

Adonis

OP

3

Noble.

You want to find two numbers that multiply to give 36, and add up to -13.

The two numbers -4 and -9 multiply to give 36 and add up to -13.

(x-9)(x-4)=0

ohhhhh

ye, ok now I remember

thank you

and thanks others too

Reply 7

Adonis

OP

3

miss_p

I think it's (x-9)(x-4)

lol

has this been the first time I have known you that you taught me something :shock:

Reply 8

Adonis

OP

3

ok, next one was just plain easy

4. Solve for x in the equation 8x2 + 120 = 320.

8x2 + 120 = 320

8x2 = 200

200/8 = 25

sqrt 25 = 5

x = 5 or -5

right?

Reply 9

Eldedu

12

x^2 -13x +36 = 0

(x-4)(x-9)= 0

x= 4
x= 9

Reply 10

Eldedu

12

Adonis

ok, next one was just plain easy

4. Solve for x in the equation 8x2 + 120 = 320.

8x2 + 120 = 320

8x2 = 200

200/8 = 25

sqrt 25 = 5

x = 5 or -5

right?

8x^2 + 120= 320

8x^2 = 200
x^2= 25

x= 5
x= -5

yep

Reply 11

Eldedu

12

any other maths probs like this you might have don't hesitate to let me know...

incidentally and just out of curiosity are you doing this for a school or uni course and if so which one?

Reply 12

Noble.

17

Adonis

ok, next one was just plain easy

4. Solve for x in the equation 8x2 + 120 = 320.

8x2 + 120 = 320

8x2 = 200

200/8 = 25

sqrt 25 = 5

x = 5 or -5

right?

Yep.

Reply 13

miss_p

8

Adonis

lol

has this been the first time I have known you that you taught me something :shock:

I don't know actually... Has it? lol

Reply 14

Adonis

OP

3

Eldedu

any other maths probs like this you might have don't hesitate to let me know...

incidentally and just out of curiosity are you doing this for a school or uni course and if so which one?

thanks buddy

uni course, maths for economics

i am revising, and starting off with the easy stuff to ease myself back into it lol

so will get progressively harder =P

Reply 15

Adonis

OP

3

Eldedu

any other maths probs like this you might have don't hesitate to let me know...

incidentally and just out of curiosity are you doing this for a school or uni course and if so which one?

ok i'm stuck again lol

QUESTIONS
1. A monopoly faces the marginal cost function MC = 0.5q2
and the marginal revenue function MR = 200 - 4q
What output will maximize profits?

so...

MR=MC that part is right

so..

200 – 4q = 0.5q2

200 = 0.5q2 + 4q

400 = q2 + 8q

ok i don't know what to do now

Reply 16

Slumpy

16

Adonis

ok i'm stuck again lol

QUESTIONS
1. A monopoly faces the marginal cost function MC = 0.5q2
and the marginal revenue function MR = 200 - 4q
What output will maximize profits?

so...

MR=MC that part is right

so..

200 – 4q = 0.5q2

200 = 0.5q2 + 4q

400 = q2 + 8q

ok i don't know what to do now

Subtract 400 from both sides, factorise.
If that's not working, do you remember the quadratic formula?

Reply 17

Adonis

OP

3

Slumpy

Subtract 400 from both sides, factorise.
If that's not working, do you remember the quadratic formula?

ok, one question about factorsing

what number am I looking to add up to?

so in this case, am I looking for 2 numbers that add up to 8? and added together add up to 8?

and i dont remember it, but i have it here in front of me

its just i haven't used it in an age, so need to get back into habit of using it ...

Reply 18

Slumpy

16

Adonis

ok, one question about factorsing

what number am I looking to add up to?

so in this case, am I looking for 2 numbers that add up to 8? and added together add up to 8?

and i dont remember it, but i have it here in front of me

its just i haven't used it in an age, so need to get back into habit of using it ...

Think of it this way:
Given the coefficient of q^2 is 1, we can factorise like this:
(q+a)(q+b)=q^2+(a+b)q+ab
So you need two numbers which add to make 8, and multiply to make -400.
A quick mental calculation suggests it probably won't work like this though, and you'll need to quadratic formula it.

Reply 19

Adonis

OP

3

raaaaaaaaaaaaaaaaah that was long lol

but I got 16.39607805437114 using the quad formula

and thats the answer in textbook [i just wanted to know how to get there]

factorization

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