For simplifying a complex rational expression we make use of copmlex conjugate( multiply and divide by the complex conjugate of the denominator).
e.g. In simplifying (1-i)/(1+i).
The complex conjugate of the denominator (1+i) is (1-i)
= (-2i)/2 as i^2=-1
` = (a-ib)/(a^2+b^2) `
`` means we multiply and devide by complex conjugate of the denomonator and simplify.
To rationalise the complex no. , we mean we want number so we can separate real and imaginary parts.
Here , so our first and last effort is that no " i " in denominator .