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`sec^2 x=(4xy)/(x+y)^2` is true if and only ifA. `x = y ne 0 `B. `x = y,x ne 0`C. `x = y`D. `x ne 0, y ne 0`

Answer» Correct Answer - (a,b)
We know that, ` sec ^(2) theta ge 1 `
` rArr " " ( 4xy )/((x + y ) ^(2)) ge 1 `
` rArr " " 4xy ge (x + y ) ^(2)`
` rArr ( x + y) ^(2) - 4xy le k 0 `
` rArr " " (x - y )^(2) le 0 `
` rArr x - y = 0 `
` rArr " " x = y `
Therefore, ` x + y = 2x " " ` [add x both sides]
But ` x + y ne 0 ` since it lies in the denominator,
`rArr 2x ne 0 `
`rArr x ne 0 `
Hence, ` x = y , x ne 0 ` is the answer.
Therefore, (a) and (b) are the answers.


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