r？ =9.42/π

∴r=√(9.42/π)=√942π / 10π

2、=√( 18×4/3×4/3)=√2×4? =4√2

3、=√(25+7)(25-7)/√27

=√(32× 18/27)

=√64×3/9)=8/3 √3

4=√( 18× 1/8×27/2)

=√(9×2×3×9/ 16)

=9/4√6