Question

If 15(2x^2-y^2)=7xy, then x:y is ?

Answer 1

\[15(2x^2-y^2)=7xy\]

Answer 2

henkjan, did you happen to solve the problem i had, cause i got an answer, and i would like to know if we had the same.

Answer 3

i dunno, but would we solve for x=0, and then x=1; and compare the results?

Answer 4

2/sqrt15

Answer 5

The answer given is 5:6

Answer 6

is x:y x wrt y tho?

Answer 7

I think yes

Answer 8

y = 0; x = ?

15(2x^2)=0; x = 0


y = 1, x = ?

15(2x^2-1)=7x

30x^2 -7x -15 = 0

x = 7 +- sqrt(1849) / 60
= 7+-43/60
= 50/60, or -36/60

i get a 5:6 in there but it might be coincident :)

Answer 9

but thats just trial and error.....lets try to find a proper method

Answer 10

trial and error IS a proper method.

Answer 11

its not eloquent and sophist uses what you know to reach what you dont ...

Answer 12

sophisticated .... im moving from typos to simply not completing words lol

Answer 13

i know amistre but fr all probs. it might not be so easy so we shuld try and find a nother method

Answer 14

that i can agree to ;)

Answer 15

lets develop some thrms

Answer 16

can we do derivatives with it?

15(2x^2-y^2) = 7xy

15(4x x' - 2y y') = 7x'y + 7xy'

60x x' - 30y = 7x' y + 7x

60x x' - 7x' y = 30y + 7x

x'(60x - 7x) = 30y + 7x

x' = (30y + 7x)/(60y - 7x)

i wonder if that helps

Answer 17

I think there must be a simpler way..

Answer 18

simpler? prolly.

Answer 19

It might be a ninth grade mathematics, Ratio and proportion

Answer 20

lol. its been like 30 years since I was in the 9th grade :)

Answer 21

30 x^2 -15x^2 = 7xy
divide by y^2 ->
30 x^2/y^2 -15 = 7x/y
30 (x/y)^2-7(x/y) = 15
use abc-formula to solve for x/y

Answer 22

what formula;btw i did same and got 2/sqrt15

Answer 23

(-7 +- sqrt(49 - 4*30*-15))/-60

(b+-sqrt(b^2-4ac)/(-2a) wasn't it?

Answer 24

no sry i got x\y=25,-18

Answer 25

I got x/y = 50/60 .. so that seems alright... or it is -0.6

Answer 26

@henkjan
I didn't understand your way of solving.

Answer 27

yeah henkjan sry am sleepy calc. mistake @abdul:quad.equation formula

Answer 28

I used the 'quadratic equation' to solve ( http://en.wikipedia.org/wiki/Quadratic_equation#Quadratic_formula).

We always call it the abc-formula here, as we rewrite an equation into
Ax^2+Bx+c =0 and solve it with this formula

Answer 29

But how did you make it into a quadratic equation?

Answer 30

You've got:

30x^2 -15y^2 = 7xy
Divide by y^2 to turn all the variables into the form (x/y)

30 (x/y)^2 - 15 = 7 (x/y)
Or:
30(x/y)^2 - 7(x/y) - 15 = 0
a = 30
b - -7
c = -15

Answer 31

I understood, Thanks everyone