Question:
To get the product 1 , we should multiply $(8 / 21)$ by
(a) $8 / 21$
(b) $-8 / 21$
(c) $21 / 8$
(d) $-21 / 8$
Solution:
(c) 21/8
Because,
$=(8 / 21) \times(21 / 8)$
$=(8 \times 21) /(21 \times 8)$
$=168 / 168$
$=1$
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