1.

If alpha,beta are the roots of equation x^(2)-10x+2=0 and a_(n)=alpha^(n)-beta^(n) then sum_(n=1)^(50)n.((a_(n+1)+2a_(n-1))/(a_(n))) is more than

Answer»

12500
12250
12750
12000

Solution :`a_(n+1)+ba_(n)+ca_(n-1)+0`
`a_(n+1)-10a_(n)+2a_(n-1)=0`
`(a_(n+1)+2a_(n-1))/(a_(n))=10`
`sum_(n=1)^(50)n.(10)=10.(50xx51)/(2)`
`=250xx51=12750`


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