数列{Xn}各项均为正,满足x1^2+x2^2+...+Xn^2=2*n^2+2*n .
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数列{Xn}各项均为正,满足x1^2+x2^2+...+Xn^2=2*n^2+2*n .
(1) 求Xn.
(2) 已知1/(x1+x2)+1/(x2+x3)+...+1/(Xn+Xn+1)=3,求n.
(3) 证明X1*X2+X2*X3+...+Xn*Xn+1
(1) 求Xn.
(2) 已知1/(x1+x2)+1/(x2+x3)+...+1/(Xn+Xn+1)=3,求n.
(3) 证明X1*X2+X2*X3+...+Xn*Xn+1
![数列{Xn}各项均为正,满足x1^2+x2^2+...+Xn^2=2*n^2+2*n .](/uploads/image/z/7721158-22-8.jpg?t=%E6%95%B0%E5%88%97%7BXn%7D%E5%90%84%E9%A1%B9%E5%9D%87%E4%B8%BA%E6%AD%A3%2C%E6%BB%A1%E8%B6%B3x1%5E2%2Bx2%5E2%2B...%2BXn%5E2%3D2%2An%5E2%2B2%2An+.)
(1)x1^2+x2^2+...+Xn^2=2*n^2+2*n
x1^2+x2^2+...+X(n-1)^2=2*(n-1)^2+2*(n-1)
Xn^2=4n Xn=2√n
(2)1/(x1+x2)+1/(x2+x3)+...+1/(Xn+Xn+1)=1/(2√1+2√2)+1/(2√2+2√3)+...+1/(2√n+2√(n+1))={(√2-√1)+(√3-√2)+...+(√(n+1)-√n)}*1/2=
1/2*(√(n+1)-1)=3 n=48
(3)X1*X2+X2*X3+...+Xn*Xn+1=2(2√1√2+2√2√3+...+2√n√(n+1))
x1^2+x2^2+...+X(n-1)^2=2*(n-1)^2+2*(n-1)
Xn^2=4n Xn=2√n
(2)1/(x1+x2)+1/(x2+x3)+...+1/(Xn+Xn+1)=1/(2√1+2√2)+1/(2√2+2√3)+...+1/(2√n+2√(n+1))={(√2-√1)+(√3-√2)+...+(√(n+1)-√n)}*1/2=
1/2*(√(n+1)-1)=3 n=48
(3)X1*X2+X2*X3+...+Xn*Xn+1=2(2√1√2+2√2√3+...+2√n√(n+1))
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