Chapter 10 - Radical Expressions and Equations - 10-2 Simplifying Radicals - Practice and Problem-Solving Exercises - Page 623: 26

$315\sqrt 2$

Solve expression and simplify: $-5\sqrt 21 \times (-3\sqrt 42)$ = $15(\sqrt 21\times \sqrt 45)$ =$ 15\sqrt 882$ Find the square factor 882= $2\times441$ = $2\times9\times49$ = $2\times 21^{2}$ So 441 is the square factor Now put it in the equation: =$ 15\sqrt 882$ =$ 15(\sqrt 2\times\sqrt 441)$ = $ 15(\sqrt 2\times\ 21)$ = $15\times21 (\sqrt 2)$ = $315 (\sqrt 2)$