The original formula = 36 10-( 1 2 3. . . . . . 77 78 79) Parentheses are similar to the practice of increasing from 65,438+0 to 65,438+000. 65,438+0 79 = 80,2,78 = 80,3,77 = 80. . . , so the bracket part is equal to (1 79)×79/2=3 160, so 36101-2-3-. . . -78-79 = 3610-3160 = 450 I hope it will help you ~