1 - 2 + 3 - 4 + 5 - 6 + 7 - 8 +......+ 456 - 457
= (1 - 2) + (3 - 4) + (5 - 6) + ...... + (455 - 456) + 457
= -1 + (-1) + (-1) + ...... + (-1) + 457
= -1 x 228 + 457
= -228 + 457
= 229
Cho A = 457 / 1 + 456 / 2 + 455 / 3 +454 / 4 + ... + 1 / 457 . Chứng minh A > 2016
Cho A=457/1+456/2+455/3+…+1/457, Chứng minh: A>2016
1+2+3+...+456+457=
Bài 1 :
a. -1 + ( -5 ) + 7 + ...+ x = 600
b. 2 + ( -4 ) + 6 + ( -8 ) +...+ = -2000
c. 1 + 2 + 3 + 4 + ... + x = 456
1-2-2-1-2-1-2-1-2-1--45-4356-42-------32423432---5-45-54535-435-34-5-35-2-5-4-52-5-54-353--3-5--5-34-5-3--4-47-87-8-787-9-76-8--34-54-6----34-3-31-4-31-423-34-1-134-41-4232-431-321------------546-3----------------2315-413-513465146-456-4-164-316361-4363411111111111111=
Bài3 tính nhanh
c. 456:2x 18+456:3-102
bài 4 tìm số tự nhiên n sao cho
121/27x 54/11<n<100/21:25/126
Bài5
x/17=60/204 6+x/33=7/11 12+x/43-x=2/3
x/5<3/7 1<11/x<2 15/26+x/16=46/52
bài6 tính nhanh
21,251+6,058+0,749+1,042 1,53+5,309+12,47+5,691
1-2-3-4-5-6-7-8-9-0+4+9+1+2+3+4+5:3:5:6:67:8:96+7+8+9+9-2-3-4-5-6-7-8-9-2+4+2+1+3+4+5+6+7+9+0+8+67?
LÂY BÚA CHAC ĐẦU ĐUÔI HỎI =?
Tính 1) 4/5 +13/18 2) 3/7 -11/8 3) -7/10 - -4/5 4) 3/20 -1/25 5) 2/3 - 5/6 6) 1/4 + -3/8 - 19/10 7) -9/10 - -7/18 8) 3/10 - 11/18 9) 3/5 -5/6 + -7/12 10) -4/9 - (-5 )/6 - 3/8
\(A=1*2*3*4*5*6*7*8*9-1*2*3*4*5*6*7*8-1*2*3*4*5*6*7*8*8\)
