October JJ

[cartera]

X+Y=1, X^2+Y^2=3, xy is less than what of the following numbers?


A. -3
B. -1
C. 0
D. 1
E. 3

[buskool]

B.

x^2 + y^2 = 3
so (x+y)^2 - 2xy = 3
now replacing (x+y) by 1.
1 - 2xy = 3
so xy = -1.

[crazy800]

it didn't ask for the value of xy, rather asked xy will be less than which value....it might be 0,1,3.....i think the question is confusing

[vgp]

Then I'm lost

It should be "more than"
just check once more

[buskool]

u r right. As vgp said. the question should be more than and then its -3 is the answer.

[genius_in_the_gene]

x+y=1
squaring
x2+y2+2xy = 1
or 3+2xy = 1
2xy = -2
xy =-1

I agree, the question should have asked about the greatest value.