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11×22+22×33+33×44+44×55+55×66+

[单选题]
11×22+22×33+33×44+44×55+55×66+66×77+77×88+88×99=()
  • 24200
  • 29040
  • 24090
  • 42200
11×22+22×33+33×44+44×55+55×66+66×77+77×88+88×99
= 11× (2 × 11+ 2×33 + 3×44+ 4×55+ 5×66 +7×88+ 8×99)
= 11× 11 (2 + 2 ×3 +3× 4+4 × 5+ 5×6 + 6× 7 + 7×8+ 8×9)
= 121× (2+6+12+20+30+42+56+72)
= 121× 240
= 29040

发表于 2020-02-22 14:31:47 回复(0)
11×11×(1×2+2×3+3×4+4×5+5×6+6×7+7×8+8×9)
发表于 2020-02-23 11:38:22 回复(0)

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