1×1⼀3加3×1⼀5加3×1⼀7等等等加17×19分之7

1×1/3加3×1/5加3×1/7等等等加17×19分之7
2025-03-22 10:02:46
推荐回答(1个)
回答1:

1/1×3+1/3×5+1/5×7+……+1/17×19
=1/2×(1-1/3+1/3-1/5+1/5-1/7+……+1/17-1/19)
=1/2×(1-1/19)
=1/2×18/19
=9/19