JAMB Mathematics 2019 Paper

3x + y = 21 ... (i);

xy = 30 ... (ii)

From (ii), $y = \frac{30}{x}$. Putting the value of y in (i), we have

3x + $\frac{30}{x}$ = 21

$\implies$ 3x$^2$ + 30 = 21x

3x$^2$ - 21x + 30 = 0

3x$^2$ - 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 = $\frac{30}{2}$ = 15;

If x = 5, y = $\frac{30}{5}$ = 6.