Question:
If a relation R is defined on the set Z of integers as follows:
$(a, b) \in R \Leftrightarrow a^{2}+b^{2}=25$. Then, domain (R) is
(a) $\{3,4,5\}$
(b) $\{0,3,4,5\}$
(c) $\{0, \pm 3, \pm 4, \pm 5\}$
(d) none of these
Solution:
(c) $\{0, \pm 3, \pm 4, \pm 5\}$
$R=\left\{(a, b): a^{2}+b^{2}=25, a, b \in Z\right\}$
$\Rightarrow a \in\{-5,-4,-3,-2,-1,0,1,2,3,4,5\}$ and
$b \in\{-5,-4,-3,-2,-1,0,1,2,3,4,5\}$
So, domain $(R)=\{0, \pm 3, \pm 4, \pm 5\}$
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