Intermediate Algebra, Chapter 5, 5.2, Section 5.2, Problem 73

Add: $(12z^2 - 11z + 8) + (5z^2 + 16z - 2) + (-4z^2 + 5z - 9)$

Remove the parentheses that are not needed from the expression.
$12z^{2}-11z+8+5z^{2}+16z-2-4z^{2}+5z-9$

Since $12z^2$ and $5z^2$ are like terms, add $5z^2$ to $12z^2$ to get $17z^2$
$17z^{2}-11z+8+16z-2-4z^{2}+5z-9$

Since $17z^2$ and $-4z^2$ are like terms, add $-4z^2$ to $17z^2$ to get $13z^2$
$13z^{2}-11z+8+16z-2+5z-9$

Since $-11z$ and $16z$ are like terms, subtract $16z$ from $-11z$ to get $5z$.
$13z^{2}+5z+8-2+5z-9$

Since $5z$ and $5z$ are like terms, add $5z$ to $5z$ to get $10z$.
$13z^{2}+10z+8-2-9$

Subtract 2 from 8 to get 6.
$13z^{2}+10z+6-9$


Subtract 9 from 6 to get $-3$.
$13z^{2}+10z-3$