If `a = log_245 175` and `b = log_1715 875`, then the value of `(1-ab)/(a-b)` is

Explanation

`175=5xx5xx7`
`245=5xx7xx7`
`875=5xx5xx5xx7`
`1715=5xx7xx7xx7`
`a(log_(5)175)/(log_(5)245)=(2+log_(5)7)/(1+2log_(5)7)`
`b=(log_(5)875)/(log_(5)1715)=(3+log_(5)7)/(1+3log_(5)7)`
Let ` log_(5)y=t`
`(1-ab)/(a-b)=(1-((2+t)/(1+2t))((3+t)/(a+3t)))/(((2+t)/(1+2t))-((3+t)/1+3t))`
`=(5t^(2)-5)/(t^(2)-1)=5`