$(x-\frac{y}{2})^{30}=a_{0}x^{30}+a_{1}x^{29}(-\frac{y}{2})+a_{2}x^{28}(-\frac{y}{2})^{2}+....+a_{30}(-\frac{y}{2})^{30}$Taco : $S=f(1;1)=(1-\frac{1}{2})^{30}=a_{0}+a_{1}(-\frac{1}{2})+a_{2}(-\frac{1}{2})^{2}+...+a_{30}(-\frac{1}{2})^{30}=(\frac{1}{2})^{30}$