A)7√8 -8√(512) -√(200)=7.√(4.2)-8.√(16.32) -√(100.2)=
=7.2.√2-8.4.√(16.2)-10√2=14√2-32.4√2-10√2=
=14√2-128√2-10√2=-124√2
b)(6-√2-√18)√2=6.√2 -√2.√2-√18.√2=6√2-2-√36=
=6√2-2-6=6√2-8
c)(5-√5)²=5²-2.5.√5+(√5)²=25-10√5+5=30-10√5
18-3х-4-2х=-6
-3х-2х=-6-18+4
-5х=-20
х=4