Question
Evaluate the following, using distributive property.
$-39 \times 99$
$-39 \times 99$
✓
Answer
$-39 \times 99 = (-40 + 1) \times (100 - 1)$
$= 40 \times (100 - 1) + 1 \times (100 - 1)$
Now, using distributive propert,
$= (-40 \times 100) + (-1 \times -40) + (1 \times 100) + (1 \times -1)$
$[\because a \times (b + c) = a \times b + a \times c]$
$= -400 + 40 + 100 - 1 = -3861$
$= 40 \times (100 - 1) + 1 \times (100 - 1)$
Now, using distributive propert,
$= (-40 \times 100) + (-1 \times -40) + (1 \times 100) + (1 \times -1)$
$[\because a \times (b + c) = a \times b + a \times c]$
$= -400 + 40 + 100 - 1 = -3861$
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