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Re: In the rectangular coordinate system, are the points (a, b) [#permalink]
Bunuel Sir,

I Didn't understand this:-

b/a=a/c->bc=ad->c/a=a/b
given a/b=c/d=cx/dx

(as the ratios are equal then there exist some for which d=cx and b=dx)
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Re: In the rectangular coordinate system, are the points (a, b) [#permalink]
Expert Reply
manojpandey80 wrote:
Bunuel Sir,

I Didn't understand this:-

b/a=a/c->bc=ad->c/a=a/b
given a/b=c/d=cx/dx

(as the ratios are equal then there exist some for which d=cx and b=dx)


a/b = c/d = cx/dx

For example: 16/32 = 2/4 = (2*8)/(4*8).
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Re: In the rectangular coordinate system, are the points (a, [#permalink]
Kinshook wrote:
mbaMission wrote:
In the rectangular coordinate system, are the points \((a, b)\) and \((c, d)\) equidistant from the origin?

(1) \(\frac{a}{b} =\frac{c}{d}\)

(2) \(\sqrt{a^2} + \sqrt{b^2} = \sqrt{c^2} + \sqrt{d^2}\)


Asked: In the rectangular coordinate system, are the points \((a, b)\) and \((c, d)\) equidistant from the origin?
Q. a^2 + b^2 = c^2 + d^2 ?

(1) \(\frac{a}{b} =\frac{c}{d}\)
a = cx; b = dx
NOT SUFFICIENT

(2) \(\sqrt{a^2} + \sqrt{b^2} = \sqrt{c^2} + \sqrt{d^2}\)
|a| + |b| = |c| + |d|
Squaring both sides
a^2 + b^2 + 2|a||b| = c^2 + d^2 + 2 |c||d|
NOT SUFFICIENT

(1) + (2)
(1) \(\frac{a}{b} =\frac{c}{d}\)
a = cx; b = dx
|a| = |x||c|; |b| = |x||d|
(2) \(\sqrt{a^2} + \sqrt{b^2} = \sqrt{c^2} + \sqrt{d^2}\)
|a| + |b| = |c| + |d|
|x||c| + |x||d| = |c| + |d|
|x| (|c| + |d|) = |c| + |d|
|x| = 1
|a| = |c|
&
|b| = |d|
a^2 + b^2 + = c^2 + d^2
SUFFICIENT

IMO C
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Re: In the rectangular coordinate system, are the points (a, [#permalink]
@Bunnel VeritasKarishma

I did this way. Could you pl. point out the mistake?

(1) + (2)

Given from St. 2: |a| + |b| = |c| + |d|

Squaring |a| + |b| = |c| + |d|, we get a^2 + b^2 + 2|ab| = c^2 + d^2 + 2|cd| ---(1)

Assuming that the question is correct, then a^2 + b^2 = c^2 + d^2

Thus, from eqn (1), we must have 2|ab| = 2|cd| => |ab| = |cd| ---(2)

From St. 1 a/b = c/d, we have a = bk and c = dk; where k is a positive int.

From eqn (2), we have b^2k = d^2k => |b| = |d|.

Now to conclude sufficient from this point?
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Re: In the rectangular coordinate system, are the points (a, [#permalink]
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jack0997 wrote:
@Bunnel VeritasKarishma

I did this way. Could you pl. point out the mistake?

(1) + (2)

Given from St. 2: |a| + |b| = |c| + |d|

Squaring |a| + |b| = |c| + |d|, we get a^2 + b^2 + 2|ab| = c^2 + d^2 + 2|cd| ---(1)

Assuming that the question is correct, then a^2 + b^2 = c^2 + d^2

Thus, from eqn (1), we must have 2|ab| = 2|cd| => |ab| = |cd| ---(2)

From St. 1 a/b = c/d, we have a = bk and c = dk; where k is a positive int.

From eqn (2), we have b^2k = d^2k => |b| = |d|.

Now to conclude sufficient from this point?




|b| = |d|

Put in |a| + |b| = |c| + |d| (from Statement 2) to get:
|a| + |b| = |c| + |b|
|a| = |c|

So we have b^2 = d^2 and a^2 = c^2 (by squaring the equations obtained)
Add to get a^2 + b^2 = c^2 + d^2
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Re: In the rectangular coordinate system, are the points (a, [#permalink]
mbaMission wrote:
In the rectangular coordinate system, are the points \((a, b)\) and \((c, d)\) equidistant from the origin?

(1) \(\frac{a}{b} =\frac{c}{d}\)

(2) \(\sqrt{a^2} + \sqrt{b^2} = \sqrt{c^2} + \sqrt{d^2}\)


Stmt-01-case-01
(a,b)=(c,d)= (2,2); ratios are same and they are equidistant.
Stmt-01-case-02
(a,b)=(50,100);(c,d)=(1,2);
Ratios are same but they are not equidistant.

Stmt-02
This can be simplified as |a|+|b|=|c|+|d|
This is will work when,
(a,b)=(c,d)= (2,3)
(a,b)=(4,1)&(c,d)= (2,3)
Hence, not sufficient.

Stmt 1&2
|a|+|b|=|c|+|d|
And
|a|*|d|=|c|*|d|
We can determine that they are equidistant or they are the same points.

Posted from my mobile device
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Re: In the rectangular coordinate system, are the points (a, [#permalink]
Bunuel wrote:
nsp007 wrote:
In the rectangular coordinate system, are the points (a, b) and (c, d) equidistant from the origin?

(1) a/b = c/d

(2) \(\sqrt{a^2}+ \sqrt{b^2} = \sqrt{c^2} + \sqrt{d^2}\)

Will post OA later.



In the rectangular coordinate system, are the points (a, b) and (c, d) equidistant from the origin?

Distance between the point A (x,y) and the origin can be found by the formula: \(D=\sqrt{x^2+y^2}\).

So we are asked whether \(\sqrt{a^2+b^2}=\sqrt{c^2+d^2}\)? Or whether \(a^2+b^2=c^2+d^2\)?

(1) \(\frac{a}{b}=\frac{c}{d}\) --> \(a=cx\) and \(b=dx\), for some non-zero \(x\). Not sufficient.

(2) \(\sqrt{a^2}+\sqrt{b^2}=\sqrt{c^2} +\sqrt{d^2}\) --> \(|a|+|b|=|c|+|d|\). Not sufficient.

(1)+(2) From (1) \(a=cx\) and \(b=dx\), substitute this in (2): \(|cx|+|dx|=|c|+|d|\) --> \(|x|(|c|+|d|)=|c|+|d|\) --> \(|x|=1\) (another solution \(|c|+|d|=0\) is not possible as \(d\) in (1) given in denominator and can not be zero, so \(d\neq{0}\) --> \(|c|+|d|>0\)) --> now, as \(|x|=1\) and \(a=cx\) and \(b=dx\), then \(|a|=|c|\) and \(|b|=|d|\) --> square this equations: \(a^2=c^2\) and \(b^2=d^2\) --> add them: \(a^2+b^2=c^2+d^2\). Sufficient.

Answer: C.

Hello Bunuel
The explanation looks great! However, I did not understand this last step-
now, as \(|x|=1\) and \(a=cx\) and \(b=dx\), then \(|a|=|c|\) and \(|b|=|d|\)
Could you please explain this in detail or with concept that has been used here?
Also, could you please tell me the difference between |a|=|c| and a = |c| or |a|=c?
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Re: In the rectangular coordinate system, are the points (a, [#permalink]
My take-

From first option, a/b=c/d=x
a=bx, c=dx
Now for two points (a,b) & (c,d) to be equidistant from origin the distance of both these points from origin (0,0) must be equal.

Distance of (a,b) from origin is sqrt(a^2+b^2)=sqrt(b^2*x^2+b^2)= b*sqrt (x^2+1)
Similarly for point (c,d) distance is d*sqrt (x^2+1).
Since we don't know whether b or d are equal from option (1) hence insufficient.

From option (2), we can derive that
a+b=c+d (I have considered them as positive for convenience), other wise it would be |a|+|b|=|c|+|d|

so putting values it would come as, b(x+1)=d(x+1), it will come as |b|=|d|
again we don't the values of b & d hence this also is insufficient.

Now combining above, putting b=d in a+b=c+d will give a=c or |a|=|c| hence the points are equidistant from origin.
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Re: In the rectangular coordinate system, are the points (a, [#permalink]
there is a quicker what to solve this:
1st statement says that a/b = c/d. what does this mean geometrically? it means that the line "r" that passes through point (a,b) and origin, and the line "s" that passes through point (c,d) and origin, have the same inclination since the tangent is the same. In other words, they lay on the same line. Is that enough to say these points are equidistant from the origin? No, because we can have one point as close as we want from the origin, and the other as distant as we want.
2nd statement says that these points belong to a family of squares in which the vertices are in the axis, and the center in the origin (just plot |x|+|y|=10 and you will see it). Is that enough to say the points are equidistant? No, because a point in the vertice is more distant than a point in the line x=y or x=-y.
But if you combine both statements, given the symmetry, it is immediate they are equidistant from the origin.
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Re: In the rectangular coordinate system, are the points (a, [#permalink]
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