Thread: Math help, determine whether equation is true

Determine whether the following statement is true for every real numbers x
and y:

(x + y)^2 = x^2 + y^2

Originally Posted by fancyface

Determine whether the following statement is true for every real numbers x
and y:

(x + y)^2 = x^2 + y^2

No!

If
x=1, y=1 it is not true.
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But let find when it is true.
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Open paranthesis,
x^2+2xy+y^2=x^2+y^2
Subtract,
2xy=0
Thus,
xy=0
Thus,
x=0
y=0

Now if we check these two we see that it is true!
So this is true only when one of them is zero.