A=101+100+99+98+...+3+2+1/101-100+99-98+...+3-2+1
101+100+99+98+...+3+2+1/101-100+99-98+...+3-2+1
S=1×2+2×3+3×4+4×5+...........+99×100
3S=1×2×3+2×3×(4-1)+3×4×(5-2)+4×5×(6-3)+............+99×100×(101-98)
3S=1×2×3+2×3×4-1×2×3+3×4×5-2×3×4+4×5×6-3×4×5+.............+99×100×101-98×99×100
3S=99×100×101
Tại sao 3S=99×100×101
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MÌNH CẢM ƠN MỌI NGƯỜI!
B=(101+100+99+98+.....+3+2+1) / (101-100+99-98+.......+3-2+1)
B=(101+100+99+98+.....+3+2+1) / (101-100+99-98+.......+3-2+1)
A] 101-100+99-98+.......+3-2+1
B] 101+100+99+98+.......+3+2+1
tinh nhanh
a) A= 33(1-2/3)(1-2/5)...(1-2/99)
b) B=101+100+99+98+...+3+2+1/101-100+99-98+...+3-2+1
c) C=423134x846267-423133/423133x846267+423134
101 +100+99+98+.........+3+2+1
101-100+99+98+.....+3-2+1
101+100+99+98+...+3+2+1
101-100+99-98+...+3-2+1