3x + y = 21 ... (i);
xy = 30 ... (ii)
From (ii), y=30x. Putting the value of y in (i), we have
3x + 30x = 21
implies 3x2 + 30 = 21x
3x2 - 21x + 30 = 0
3x2 - 15x - 6x + 30 = 0
3x(x - 5) - 6(x - 5) = 0
(3x - 6)(x - 5) = 0
3x - 6 = 0 implies x = 2.
x - 5 = 0 implies x = 5.
If x = 2, y = 302 = 15;
If x = 5, y = 305 = 6.
