1 + 2 - 3 -4 + 5 + 6 -7 -8 + ... +97 +98 -99 -100 ( có: ( 100 - 1 ) : 1 + 1 = 100 )
= ( 1 +2 - 3 - 4 ) + ( 5 + 6 - 7 -8 ) + ... ( 97 + 98 - 99 +100 ) ( có 100 : 4 = 25 cặp )
= - 4 + -4 + -4 + ... + -4 ( có 25 số hạng )
= ( -4 ) . 25
= -100
Tính A=92-1/9-2/10-3/11-4/12-5/3-...-91/99-92/100 / 1/45+1/50+1/55+...+1/495+1/500
A=100+98+96+94+...+2-97-95-93-91-...-1
B=1+2-3-4+5+6-7-8+9+10-11-12+...+...-299-300+301+302
số 2 : tính nhanh
A = 99 - 97 + 95 -93 + 91 - 89 + .......... + 7 - 5 + 3 - 1
B = 50 - 49 + 48 - 47 + 46 - 45 + ........... + 4 - 3 + 2 - 1
C = 100 + 98 + 96 + ......... + 2 - 97 - 95 - ......... - 1
D = 1 + 3 + 5 + 7 + ......... + 999
E = 1 + 11 + 21 + 31 + ......... + 991
F = 3 + 7 + 11 + 15 + ......... + 99
H = 1 + 2 + 3 - 4 - 5 - 6 + 7 + 8 + 9 - 10 - 11 - 12 + .......... + 97 + 98 + 99 - 100 -101 - 102
I = 1 - 3 + 5 5 - 7 + 9 - 11 + ... + 2004 - 2007
K = -1 + 2 - 3 + 4 - 5 + 6 - 7 +.... + 2004 - 2005
G =1 - 2 - 3 + 4 + 5 - 6 - 7 + 8 +..... + 2004 + 2005
N = 1 - 4 + 7 - 10 + ..... + 2995 - 2998
Tính 1-2-3-4-5-6-7-8-9-10-...90-91-92-93-94-95-96-97-98-99
Tính hợp lý
\(A= (\dfrac{92-\dfrac{1}{9}-\dfrac{2}{10}-\dfrac{3}{11}-...-\dfrac{91}{99}-\dfrac{92}{100}}{\dfrac{1}{45}+\dfrac{1}{50}+\dfrac{1}{55}+...+\dfrac{1}{495}+\dfrac{1}{500}}\) B= \(\dfrac{\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{8}+\dfrac{1}{9}+\dfrac{1}{10}}{\dfrac{1}{9}+\dfrac{2}{8}+\dfrac{3}{7}+...+\dfrac{8}{2}+\dfrac{9}{1}})\)
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
Tính A :=1+2-3-4+5+6-7-8+9+10-11-12+...+97+98-99-100
Tính:
1+2+3+4+5+6+7+8+9+10+...+91+92+93+94+95+96+97+98+99+100=?
Tính bằng cách nhanh nhất (có cách trình bày)
bài 91(SBT 6 trang 27)
M=8/3 . 2/5 . 3/8 . 10 . 19/92
N=5/7 . 5/11 + 5/7 . 2/11 - 5/7 .14/11
Q=(1/99 + 12/999 + 123/9999) . 1/2 -1/3 -1/6)
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