1.

If a, b are postitive real numbers such that ab=1, then the least value of the expression `(1+a)(1+b)` isA. 2B. 3C. 4D. none of these.

Answer» Correct Answer - C
We have, `ab=1impliesb=(1)/(a)`
`:." "(1+a)(1+b)=(1+a)(1+(1)/(a))`
`implies" "(1+a)(1+(1)/(a))=2+a+(1)/(a)ge2+2=4" "[because a+(1)/(a)ge2]`
Hence, the least value of `(1+a)(1+b)` is 4.


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