## Algebra: A Combined Approach (4th Edition)

$x^{4}-1$
$18x^{4}+2x^{3}y^{3}-1-2y^{3}x^{3}-17x^{4}$ Rewrite this expression by putting the $x$ of the fourth term right after the coefficient: $18x^{4}+2x^{3}y^{3}-1-2x^{3}y^{3}-17x^{4}=...$ Simplify the expression by combining like terms: $...=(18-17)x^{4}+(2-2)x^{3}y^{3}-1=...$ $...=x^{4}+(0)x^{3}y^{3}-1=...$ $...=x^{4}-1$