1×1+2×2+3×3+4×4+5×5+6×6.20×20
1/1*3+1/2*4+1/3*5+1/4*6+.+1/18*20
{3/4+4/5+5/6}+{1+2/3+3/4+4/5}-{1+2/3+3/4+4/5+5/6}×{2/3+3/4+4
1×2+2×3+3×4+4×5+5×6+……+19×20
1-2+3-4+5-6~~+19-20+21
简算(1)20-1/4×2/5 5/6 (2) (7/16 4/5)÷3/5 (3
(1)(1+2/3+3/4+4/5+5/6)*(1+3/4+4/5)-(1+3/4+4/5)*(2/3+3/4+4/5+
1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1 1 6 15 20 15 6 1
7/9*5/6/14/27 1/2*2/5+9/10/9/20 5/8*1/4/5/8*1/4 (1/2+2/3+3/4
:(1/2+2/3+3/4+4/5+5/6+6/7)+(1/2+2/3+3/4+4/5+5/6+6/7)*1/2—(1+
1+2+3+4+5+6+7+8+9+10-50+20-25+1+4+5
(1\2+1\3)+(2\3+1\4)+(3\4+1\5)+(4\5+1\6)+.+(18\19+1\20)+(19\2
1*2*3*4+2*3*4*5+3*4*5*6+.+17*18*19*20=?