Chapter 5 - Mid-Chapter Check Point - Page 378: 1

$-55x^{4}y^{6}$

Mulyiplying the constants and multiplying the variables, the product of the given expression, $ (11x^2y^3)(-5x^2y^3) ,$ is \begin{array}{l}\require{cancel} 11(-5)x^{2+2}y^{3+3} \\\\= -55x^{4}y^{6} .\end{array}