38.和是多少
1
(1) 1×3
+ 1 +...+ 3×5
1
97×99
= 1 2 +
2 +...+ 2
2 1×3
3×5 97×99
= 1 1 1 1 1 1
2 (1 − 3) + ( 3 − 5)+...+( 97 − 99 )
= 1 1
2 1 − 99
= 49
99
(2)-(4)略
1
(1) 1×3
+ 1 +...+ 3×5
1
97×99
= 1 2 +
2 +...+ 2
2 1×3
3×5 97×99
= 1 1 1 1 1 1
2 (1 − 3) + ( 3 − 5)+...+( 97 − 99 )
= 1 1
2 1 − 99
= 49
99
(2)-(4)略