- #1
Jamin2112
- 986
- 12
Prove that if x and y are ...
Prove that if x and y are distinct real numbers, then (x+1)2=(y+1)2 if and only if x+y=-2. How does the conclusion change if we allow x=y?
...
Suppose x and y are real numbers. If x≠y then
x+2≠y+2
----> (x+2)/(y+2)≠1
----> (x+2)/(y+2)≠ x/y or y/x (since x/y=y/x=1)
----> (x+2)x=(y+2)y
or
(x+2)/x=(y+2)/y
----> (x+2)x=(y+2)y (since (x+2)/x=(y+2)/y ---> x=y)
----> x2+2x=y2+2y
---->x2+2x+1=y2+2y+1
---->(x+1)2=(y+1)2
----> x+1 = (y+1) or (-y-1)
----> x+1=-y-1 (since x+1=y+1 ---> x=y)
----> x+y=-2
?
But I'm not sure if I've done everything it asked. I know for "P if and only Q," it needs to be proven that P--->Q and Q--->P, but it seems here that if P is (x+1)2=(y+1)2 and Q is x+y=-2, I'm just kind of going in circles by proving the "if and only if" part. See what I'm saying?
Homework Statement
Prove that if x and y are distinct real numbers, then (x+1)2=(y+1)2 if and only if x+y=-2. How does the conclusion change if we allow x=y?
Homework Equations
...
The Attempt at a Solution
Suppose x and y are real numbers. If x≠y then
x+2≠y+2
----> (x+2)/(y+2)≠1
----> (x+2)/(y+2)≠ x/y or y/x (since x/y=y/x=1)
----> (x+2)x=(y+2)y
or
(x+2)/x=(y+2)/y
----> (x+2)x=(y+2)y (since (x+2)/x=(y+2)/y ---> x=y)
----> x2+2x=y2+2y
---->x2+2x+1=y2+2y+1
---->(x+1)2=(y+1)2
----> x+1 = (y+1) or (-y-1)
----> x+1=-y-1 (since x+1=y+1 ---> x=y)
----> x+y=-2
?
But I'm not sure if I've done everything it asked. I know for "P if and only Q," it needs to be proven that P--->Q and Q--->P, but it seems here that if P is (x+1)2=(y+1)2 and Q is x+y=-2, I'm just kind of going in circles by proving the "if and only if" part. See what I'm saying?