The restriction of the expression as given in the task content is; x +y = 0.
What is the restriction of the expression?
The expression in the task content is rational;
(1-x-y)/(x+y).
On this note, the restriction to the expression is the values which render the denominator of the expression equal to 0 and consequently the expression value to undefined.
Hence, the restriction is; x+y = 0.
Read more on undefined rational function;
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