Equations

[niraj_a]

If x^2/9 - 4/y^2 = 12, what is the value of x?

(1) x/3 + 2/y = 6

(2) x/3 - 2/y = 2

Those blobs stand for negative

[Naruto]

IMO D

Each alone is sufficient,
the equation is of form a^2-b^2, i.e (a+b) x (a-b)

if a+b is given we can find value of a-b and then solving the two the value of a

Same goes for a-b.

[niraj_a]

i see naruto. here's my question though -

say in 1) we arbitrarily square the whole string, so we get

x^2/9 + 4/y^2 = 36

so we add the stem and this result to get

2(x^2/9) = 36
(x^2) = 2
so x = + or - 1.41

the same issue happens if you square statement 2. where did i go wrong? it doesnt say anywhere is x or y are integers or -ve.

[KK9_GMAT]

niraj_a,

When you square 1) ie. (x/3 + 2/y)^2 = 6^2,
using (a+b)^2 = a^2 + 2ab + b^2

we get, (x^2/9) + 2((x/3)*(2/y)) + (4/y^2) = 36
(x^2/9) + (4x/3y) + (4/y^2) = 36

which is not equal to what you calculated.
I think this is where you might have gone wrong.

[niraj_a]

kudos, thanks much.

i guess i'll never score high on the quant....

[KK9_GMAT]

No worries. Better to commit mistakes now than in the actual exam.

[vikram_k51]

If x^2/9 - 4/y^2 = 12, what is the value of x?

(1) x/3 + 2/y = 6

(2) x/3 - 2/y = 2

Those blobs stand for negative

Answer will be D.

[fruti_yum]

If x^2/9 - 4/y^2 = 12, what is the value of x?

(1) x/3 + 2/y = 6

(2) x/3 - 2/y = 2

Those blobs stand for negative

Answer will be D.

When i solve each of the statements , i get either y = 6 or x = 12 for both individually..

Where do i go from there in the question stem?