(-2)^50*(0.5)^51=(-2)*(-2)*(-2)*...*(-2)*(0.5)*(0.5)*...*(0.5)=[(-2)*(0.5)]*[(-2)*(0.5)]*...*[(-2)*(0.5)]*0.5=(-1)*(-1)*...*(-1)*0.5=(-1)*0.5=-0.5
（-2）^50*(0.5)^51=2^50*2^(-51)=2^(50-51)=2^-1=0.5
