a)
x= √162 -√242 + √288 - √98 + √18 =
= 9√2 -11√2 + 12√2 - 7√2 + 3√2 =
=24√2-18√2=6√2
y= √320 +√20 - √500 + √125 - √180=
= 8√5 +2√5 - 10√5 + 5√5 - 6√5=
= 15√5 - 16√5 = -√5
b x=6√2=√72
√64<√72<√81
8 < 6√2 > 9
x*y=6√2*(-√5)=-6√10
-6√10 =-√360
-√361<-√360 <-√324
-19 < -6√10 < -18
x*y∈(-19,-18)