Bn=b1*q^n-1
b3=b1*q^2
18=b1*9
b1=2
<span>S5=2(1-243)/1-3 = -484/-2=242</span>
<em>Ответ и решение во вложении</em>
√(11+6√2)=√(3²+2*3*√2+(√2)²)=√(3+√2)²=3+√2
√(11-6√2)=√(3²-2*3*√2+(√2)²)=√(3-√2)²=3-√2
(√(11+6√2))²-(√(11-6√2))²=(3+√2)²-(3-√2)²=(3+√2-3+√2)(3+√2+3-√2)=
=2√2*6=12√2