(1)5√2+√8-7√8
=5√2+2√2-14√2
=-7√2
(2)2√5×(-3√45)-(√6+2)²
=-2√5×9√5-(6+4√6+4)
=-90-10-4√6
=-100-4√6
(3)√12-√½-2√(1/3)
=2√3-√2/2-2√3/3
=4√3/3-√2/2
=(8√3-3√2)/6
(4)y=√(x-3)+√(3-x)+8
∵x-3≥0,3-x≥0
∴x=3
∴y=8
x+3y=3+3×8=27
∴x+3y的立方根是3
(1)5√2+√8-7√8
=5√2+2√2-14√2
=-7√2
(2)2√5×(-3√45)-(√6+2)²
=-2√5×9√5-(6+4√6+4)
=-90-10-4√6
=-100-4√6
(3)√12-√½-2√(1/3)
=2√3-√2/2-2√3/3
=4√3/3-√2/2
=(8√3-3√2)/6
(4)y=√(x-3)+√(3-x)+8
∵x-3≥0,3-x≥0
∴x=3
∴y=8
x+3y=3+3×8=27
∴x+3y的立方根是3