r^2-r+(1/4)sin^2 4 theta is not an equation because there's no equal sign. Is it supposed to equal 0? If so, do you know how to factor a quadratic equation?
You can factor it. Does it make sense that if a and b are the roots of the equation, r^2-r+(1/4)sin^2 4 theta can be factored into A(r-a)(r-b)? You can find a and b using the quadratic formula. You won't get a numerical answer, but you will get an expression for a and b in terms of theta.