Concept:The equation of line in intercept form is\(\displaystyle \frac{x}{a}+\frac{y}{b}=1\), where a and b are the intercept made on the x and y-axis.Calculation:The equation of line in intercept form is? \(\displaystyle \frac{x}{a}+\frac{y}{b}=1\)Given, the line cuts off equal intercepts. So a = b? \(\displaystyle \frac{x}{a}+\frac{y}{a}=1\)? x + y = a ------(i)It passes through (1, -2).So 1 “ 2 = a? a = -1? x + y = -1 [from (i)]? x + y + 1 = 0? x + y + 1 = 0 is the required equation.