( 1)
2+4+6+8+ 10+ 12+ 14+ 16+ 18+20
= (2+20)+(4+ 18) +(6+ 16)+(8+ 14)+( 10+ 12)
= 22×5
= 1 10
(2)
20- 19+ 18- 17+ 16- 15+ 14- 13+ 12- 1 1+ 10-9+8-7+6-5+4-3+2- 1
= (20- 19)+( 18- 17)+( 16- 15)+( 14- 13)+( 12- 1 1)+( 10-9)+(8-7)+(6-5)+(4-3)+(2- 1)
= 1× 10
= 10
I will fill it out.
In the formula with brackets, the plus sign is in front of the brackets, and the brackets are removed (the numbers in brackets are the same symbol); Put parentheses after the plus sign and put (the number of) in parentheses; The minus sign is in front of the brackets, and the brackets (number symbols in brackets) are removed; Parentheses are added after the minus sign, in parentheses (the number of symbols will change).