q48
- Option : C
- Explanation : ∴ x-y=4 =>x=4+y
and 1/x+1/y=10/21
=1/4+y+1/y=10/21 =>y+4+y/y24y=10/21=> 42y+ 84 = lOy2 + 40y
=> lOy2 - 2y - 84 = 0 => 5y2 -y- 42 = 0
=> 5y2 -15y+ 14y- 42 = 0
=> 5y(y -3) + 14(y - 3) = 0
∴ y = 3
=> 42y+ 84 = lOy2 + 40y
=> lOy2 - 2y - 84 = 0 => 5y2 -y- 42 = 0
=> 5y2 -15y+ 14y- 42 = 0
=> 5y(y -3) + 14(y - 3) = 0
∴ y = 3
