You have already been told that several times. You appear to have extreme difficulty understanding the responses you get.
You have been told repeatedly that the magnitude is r= 5 and that the argument (or amplitude), angle, is . The polar form is either or . Your equation is . .
However, your original question was to find the square roots of 3+ 4i and bigwave, in his first response, showed you how to do that without using the polar form.