(1-1/2^2)(1-1/3^2).(1-1/49^2)(1-1/50^2)=(1+1/2)(1-1/2)(1+1/3)(1-1/3)……(1+1/49)(1-1/49)(1+1/50)91-1/50)=(3/2x4/3x……x50/49x51/50)x(1/2x2/3x……x48/49x49/50)=51/2x1/50=51/100