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Hi Bunuel,

What I did is, calculating the 4 possibilities:


1- X+3=4X-3 ,then X=2
2- X+3= -(4X-3) = -4X+3, then X=0
3- Y+1=3, then Y=2
4- Y+1=-3, then Y=-4

When I tried to plug in all the outcomes, then all give a correct answers including 0 (0+3=-4(0)+3) so 0+3=0+3)

So, what's wrong here?
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If |x + 3| = 4x - 3 and |y + 1| = 3, and x y, what is the product of the unique solutions for x and y?

A. -16
B. -8
C. -4
D. 0
E. 4

We’re given |x + 3| = 4x - 3

Since the left-hand side is an absolute value, it must be non-negative. So the right-hand side must also be non-negative:

4x - 3 ≥ 0, which gives x ≥ 3/4

If x ≥ 3/4, then x + 3 > 0, so |x + 3| = x + 3

Now the equation becomes x + 3 = 4x - 3, which gives x = 2.

Next, |y + 1| = 3. That gives two cases: y + 1 = 3 or y + 1 = -3, so y = 2 or y = -4

Since x ≠ y and x = 2, we must take y = -4

Then the product is x * y = 2 * (-4) = -8

Answer: B
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Hi Bunuel,

What I did is, calculating the 4 possibilities:


1- X+3=4X-3 ,then X=2
2- X+3= -(4X-3) = -4X+3, then X=0
3- Y+1=3, then Y=2
4- Y+1=-3, then Y=-4

When I tried to plug in all the outcomes, then all give a correct answers including 0 (0+3=-4(0)+3) so 0+3=0+3)

So, what's wrong here?
Bunuel
ccarson
If |x + 3| = 4x - 3 and |y + 1| = 3, and x y, what is the product of the unique solutions for x and y?

A. -16
B. -8
C. -4
D. 0
E. 4

We’re given |x + 3| = 4x - 3

Since the left-hand side is an absolute value, it must be non-negative. So the right-hand side must also be non-negative:

4x - 3 ≥ 0, which gives x ≥ 3/4

If x ≥ 3/4, then x + 3 > 0, so |x + 3| = x + 3

Now the equation becomes x + 3 = 4x - 3, which gives x = 2.

Next, |y + 1| = 3. That gives two cases: y + 1 = 3 or y + 1 = -3, so y = 2 or y = -4

Since x ≠ y and x = 2, we must take y = -4

Then the product is x * y = 2 * (-4) = -8

Answer: B

x = 0 doe not satisfy |x + 3| = 4x - 3. As said in the solution you quote, x must be more than or equal to 3/4.
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very important to note that x is not equal to y. else the answer will be wrong
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If |x + 3| = 4x - 3 and |y + 1| = 3, and x y, what is the product of the unique solutions for x and y?

Inflection points:
x = -3; y = -1

Case 1: x < -3; y< -1
-3-x = 4x - 3; x = 0; But x<-3; Not feasible

Case 2: x < -3; y>=-1
-3-x = 4x - 3; x = 0; But x<-3; Not feasible

Case 3: x >= -3; y<-1
x+3 = 4x -3; x = 2
-y-1 = 3; y=-4;
xy = 2*(-4) = -8; Feasible

Case 4: x >= -3; y>=-1
x+3 = 4x -3; x = 2
y+1=3; y =2;
xy = 2*2 = 4; Not unique values of x & y; Not feasible

IMO B
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