Proof

[Gabrielle]

I need to prove this proof incorrect, but I don't know how, please help.

Let x=y
Xy=x^2
xy-y^2=x^2-y^2
y(x-y)=(x+y)(x-y)
Y=x+y

Let x=1
y=1

1=1+1
1=2

 

[Someone2841]

I need to prove this proof incorrect, but I don't know how, please help.

Let x=y
Xy=x^2
xy-y^2=x^2-y^2
y(x-y)=(x+y)(x-y)
Y=x+y

Let x=1
y=1

1=1+1
1=2

\(\displaystyle x=y \to x-y=0\)

\(\displaystyle y(x-y) = (x+y)(x-y) \to y = x+y\) is accomplished only by divided by \(\displaystyle x-y\).

Division by zero is undefined.

 

[lookagain]

I need to prove this proof incorrect, but I don't know how, please help.

Let x=y

\(\displaystyle \longrightarrow\)Xy=x^2

xy-y^2=x^2-y^2

y(x-y)=(x+y)(x-y)

\(\displaystyle \longrightarrow\)Y=x+y

Let x=1
y=1
\(\displaystyle \cdot\)
\(\displaystyle \cdot\)
\(\displaystyle \cdot\)

Gabrielle,

"X" is not the same variable as "x," and "Y" is not the same variable as "y."

From the beginning, use either the lower case or upper case of that letter,
but not both, for a particular variable and stick with it.