1/1-1/2+1/2-1/3+1/3-1/4+...+1/19-1/20
=1/1-1/20=19/20
1/1-1/2+1/2-1/3+1/3-1/4+...+1/19-1/20
=1/1-1/20=19/20
1/2×3+1/3×4+1/4×5+....+1/18×19+1/19×20
Tính : A = 1/1*2 + 1/2*3 + 1/3*4 + ........ 1/18*19 + 1/19*20
Trả lời : A = ..............
1/2 nhân 3 + 1/3 nhân 4 + 1/4 nhân 5 + ... + 1/18 nhân 19 + 1/19 nhân 20
tính nhanh]
b)\(\frac{1\cdot10+2\cdot19+3\cdot18+4\cdot17+.....+18\cdot3+19\cdot2+20\cdot1}{20\cdot\left(1+2+3+.....+19+20\right)-\left(1\cdot2+2+3+3\cdot4+.....+19\cdot20\right)}\)
(1-1/2)*(1-2/3)*(1-3/4)*...*(1-1/18)*(1-1/19)*(1-1/20)
(1/2×3+1/3×4+1/4×5) :19/20×2014×+1=2014
mong moi nguoi giup do minh dang can gap
a , 1/2+1/4+1/8+1/16+1/32
b , 2/1*2+2/2*3+2/3*4+...+2/18*19+2/19*20
E=1*2+2*3+3*4+...+18*19+19*20 = ?
Cho biểu thức:
A=1/2×3+1/2×3×4+1/3×4×5+…+1/18×19×20
Hãy so sánh A và 1/4