Question
Expand $: (a - 2b - 3c)^2$
✓
Answer
$(a - 2b - 3c)^2 $
$= [a + (-2b) + (-3c)]^2 $
$=(a)^2+ (-2b)^2 + (-3c)^2 + 2(a)(-2b) + 2(-2b)(-3c) + 2(a)(-3c)$
$=a^2 + 4b^2 + 9c^2 - 4ab + 12bc - 6ac$
$= [a + (-2b) + (-3c)]^2 $
$=(a)^2+ (-2b)^2 + (-3c)^2 + 2(a)(-2b) + 2(-2b)(-3c) + 2(a)(-3c)$
$=a^2 + 4b^2 + 9c^2 - 4ab + 12bc - 6ac$
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