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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` | 
                            
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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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