Let the equation of the line be $\frac{x}{a}+\frac{y}{b}=1$
This line passes through $(3,4)$
$\frac{3}{a}+\frac{4}{b}=1$
Since the sum of the intercepts of the line is zero,
$ a+b=0$
$a=-b . \ldots . \text { (iii) } $
Substituting the value of $a$ in (ii), we get
$ \frac{3}{b}+\frac{4}{b}=1$
$\frac{1}{b}=1$
$b=1$
$a=-1 \ldots . .[\text { From (iii)] } $
Substituting the values of $a$ and $b$ in (i), the equation of the required line is
$ \frac{x}{-1}+\frac{y}{1}=1$
$x-y=-1$
$\therefore x-y+1=0 $
Case II: Line passing through origin.
Slope of line passing through origin and $A(3,4)$ is
$m=\frac{4-0}{3-0}=\frac{4}{3}$
Equation of the line having slope $m$ and passing through origin $(0,0)$ is $y=m x$.
The equation of the required line is
$ y=\frac{4}{3} x$
$\therefore 4 x-3 y=0 $
$\therefore$ There are two lines which pass through $A (3,4)$ and the sum of whose intercepts is zero.



