Question
$99 \times 101$ can be written as $(100 - 1) \times (100 + 1).$
✓
Answer
$\because 99 \times 101 = 9999$ and $(100 - 1) \times (100 + 1)$
$= 100 \times (100 + 1) -1 \times (100 + 1)$
$= 100 \times 100 + 1 \times 100 - 1 \times 100 -1 \times 1 [$using distributive property$]$
$= 10000 + 100 - 100 -1 = 9999$
$= 100 \times (100 + 1) -1 \times (100 + 1)$
$= 100 \times 100 + 1 \times 100 - 1 \times 100 -1 \times 1 [$using distributive property$]$
$= 10000 + 100 - 100 -1 = 9999$
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