θn+1=θn−xtsin2θn−2ytcos2θn−gx2t/v202xtcos2θn+2ytsin2θn Then plug this θ0 into ...θn+1=θn−xtsin2θn−2ytcos2θn−gx2t/v202xtcos2θn+2ytsin2θn Then plug this θ0 into the right-hand side, which returns θ1; for the next iteration, plug this θ1 into the right-hand side, which returns θ2, etc.