Ta có A = \(\left(1-\frac{1}{3}\right).\left(1-\frac{1}{6}\right).\left(1-\frac{1}{10}\right)...\left(1-\frac{1}{780}\right)\)
= \(\frac{2}{3}.\frac{5}{6}.\frac{9}{10}...\frac{779}{780}=\frac{4}{6}.\frac{10}{12}.\frac{18}{20}...\frac{1558}{1560}=\frac{1.4}{2.3}.\frac{2.5}{3.4}.\frac{3.6}{4.5}...\frac{38.41}{39.40}=\frac{\left(1.2.3...38\right).\left(4.5.6...41\right)}{\left(2.3.4...39\right).\left(3.4.5...40\right)}\)
= \(\frac{1.41}{39.3}=\frac{41}{117}\)
Tính nhanh:
A=10 - 1/72 - 1/50 - 1/42- .... - 1/6 - 1/2
Tìm x:
a.(x+1) + (x+1/3) +(x+1/6) +...+(x+1/55)= 130/11
b. 2/3.x - 780/11 :(13/15 +13/3535+13/63+1313/9999) +5=0
c. 2012/77 +20112/165 +2012/258 +2012/437=16/161 .x
Cảm ơn nhiều!!!!!!!!!!!
Bài1.Tính nhanh:
(1-1/3)x(1-1/6)x(1-1/10)x...........(1-1/780)
giup minh nha. mai minh phai nop bai nay roi.
Tính hợp lí:
a) A=1+1/2x(1+2)+1/3x(1+2+3)+...+1/2016x(1+2+...+2016)
b)B=1/10+1/40+1/88+1/54+1/268
c)(1-1/3)x(1-1/6)x...x(1-1/780)
(1-1/3)x(1-1/6)x...(1-1/780)
(x+2)5 = 210
1+2+3+...+x=78
(x+1)2=(x+1)0
(2+x)+(4+x)+(6+x)+...+(52+x)=780
tim x :
a) (3x - 4) . (x- 1)3 = 0
b) x17 = x
c) 22x - 1 : 4 = 83
d) (x + 2)5 = 210
e) (X - 5)4 = (X - 5)6
f) 1+2+3+.......+x =78
g) (x +1)2 =(x +1)0
h) (2 + x) + (4 +x) + ( 6 +x) +.......+(52 + x)= 780
Tìm x
Trả lời nhanh giúp mình nha, mnh đang rất vội, cảm ơn.
Tính nhanh
1/3 + 1/6 + 1/10 +....+ 1/x(x + 1) = 1 + 1991/1993
Tính nhanh
a,8/9.15/16.24/25.....2499/2500
b,(1-1/3)(1-1/6)(1-1/10)(1-1/15).....(1-1/780)
1.Tính tổng
a, A= 1/2 + 1/6 + 1/12 +...+ 1/n x (n+1)
b, B= 1 x 2 x 4 + 1/4 +...+ 1/9 x 100
2.Cho A= 1/4 x 3/6 x 5/8 x...x 43/46 x 45/48
B= 2/5 x 4/7 x 6/9 x...x 46/49
a, So sánh A và B
b, Cmr A <1/133
3.Tìm số TN x biết,
a, 10 + x/ 17 + = 3/5
b, 40 + x/ 77 - x = 6/7
4. Tìm số TN a,b biết:
a/b = 24/26
a, BCNN(a,b) = 1092
5.Tính nhanh
a, A= (1 - 1 = 2) x (1 - 1 = 3) x (1 - 1 = 4) x...x (1 - 1 = 20)
b, B= (1/3 - 1) x (1/6 - 1) x (1/10 - 1) x (1/15 -1)
c, D= (1 + 6/8) x (1 + 6/18) x ( 1+ 6/30)
