3√7=√7+2√7=4√7-√7=3*√7=21:√7
8+√5=8+√5=(10+√5)-2= 2 *(4+√5/2)= (64-5)/(8-√5)
-2+√3=( -2)+√3=√3- (+2)=-2* (1-√3/2)=(3-4)/ (√3+2)
-7,5=-7+ (-0,5)=0,5 - (+8)=-2,5*3=15 / (-2)
18=9+9=20-2=2*9= 38:2
√6-√11= √6 + (-√11)=√6-(+√11)= (1/2)*( 2√6-2√11)= (6-11)/(√6+√11)