Intercept form of a straight line is x/a + y/b = 1,
Where a and b are the intercepts on the axis
Given that a = b,
∴ x/a + y/b = 1 ... (1)
If equation (1) passes through the point (1, -2) we get
So, equation of the straight line is x y
Hence, the required equation x + y + 1 = 0
