Question
How much is $21 a^3-17 a^2$ less than $89 a^3-64 a^2+6 a+16$ ?
✓
Answer
Required expression is
$89 a^3-64 a^2+6 a+16-\left(21 a^3-17 a^2\right)$
$=89 a^3-64 a^2+6 a+16-21 a^3+17 a^2$
On combining the like terms,
$=89 a^3-21 a^3-64 a^2+17 a^2+6 a+16$
$=68 a^3-47 a^2+6 a+16$
So,
$21 a^3-17 a^2 \text { is } 68 a^3-47 a^2+6 a+16 \text { less than } 89 a^3-64 a^2+6 a+16$.
$89 a^3-64 a^2+6 a+16-\left(21 a^3-17 a^2\right)$
$=89 a^3-64 a^2+6 a+16-21 a^3+17 a^2$
On combining the like terms,
$=89 a^3-21 a^3-64 a^2+17 a^2+6 a+16$
$=68 a^3-47 a^2+6 a+16$
So,
$21 a^3-17 a^2 \text { is } 68 a^3-47 a^2+6 a+16 \text { less than } 89 a^3-64 a^2+6 a+16$.
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