1.

If a and b are positive real numbers other than unity, then the least value of `|"log"_(b) a + "log"_(a) b|`, is

Answer» Correct Answer - C
We have,
`|"log"_(b) a + "log"_(a)b|`
`=|"log"_(b)a +(1)/("log"_(b)a)| = |x + (1)/(x)|, "where " x = "log"_(b)a,`
We know that
`x+ (1)/(x) ge 2 " for all" x gt 0 " and ", x + (1)/(x) le -2 " for all" x lt 0`
`therefore |x + (1)/(x)| ge 2 " for all" x ne0`
`therefore |"log"_(b)a + "log"_(a)b| ge 2`
Hence, the least value of `|"log"_(b)a + "log"_(a)b|` is 2.


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