You didn't say it was difficult. Let me put it briefly: sum:1/2+1/4+1/8+116+(infinite term) University: use the limit solution. Sum formula of proportional sequence: 1-( 1/2) n n approaches positive infinity, so =1; High school: use reflective solutions. Let the sum result of the original formula be s, then the solution of 1/2+s/2=s is s= 1.