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If `a ,b ,c`are three distinct real numbers in G.P. and `a+b+c=x b ,`then prove that either x < -1 or x > 3

Answer» `a+b+c = xb`
`=>xb-b = a+c`
`=>b(x-1) = a+c`
`=>x-1 = (a+c)/b`
As, `a,b,c` are in G.P,
`:. b^2 = ac => b = sqrt(ac).``:. x-1 = (a+c)/(sqrt(ac))`
`=>x -1 = sqrt(a/c)+sqrt(c/a)`
Now, we know, `m+1/m gt 2` or `m+1/m lt -2.`
`:. sqrt(a/c)+sqrt(c/a) gt 2 or sqrt(a/c)+sqrt(c/a) lt -2.`
`:. x - 1 gt 2 or x-1 lt -2`
`=>x gt 3 or x lt -1.`


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