Algebra and Trigonometry 10th Edition

(a) $6$ (b) $3x^2$
(a) Using property 2 (page 19): $\sqrt {12}\sqrt 3=\sqrt {12\times3}=\sqrt {36}=6$ (b) Using properties 6 (page 19): $\sqrt[4] {(3x^2)^4}=|3x^2|=3x^2$ Obs: $3x^2\geq0$ for any value of $x$, so: $|3x^2|=3x^2$