Gọi\(A=\dfrac{1}{3}+\dfrac{1}{3^2}+...+\dfrac{1}{3^8}\)
\(\Rightarrow3A=1+\dfrac{1}{3}+\dfrac{1}{3^2}+...+\dfrac{1}{3^7}\)
\(\Rightarrow2A=\left(1+\dfrac{1}{3}+...+\dfrac{1}{3^7}\right)-\left(\dfrac{1}{3}+\dfrac{1}{3^2}+...+\dfrac{1}{3^8}\right)\)
\(\Rightarrow2A=1-\dfrac{1}{3^8}\)
\(\Rightarrow A=\dfrac{1}{2}-\dfrac{1}{3^8.2}\)
tìm x biết
a. 2x-1/3=3x+2/5
b.2/3*=8/27
c.2 nhân 1/2*+3 nhân 1/2*+1=7/8
Tìm X biết:
a/ -2/3 : x + 5/8=-7/12
b/ -1/2+1/2 x X = -2/3 -3
1. Cho \(b^2=ac\) ; \(c^2=bd\)
Chứng minh rằng :
\(\dfrac{a^3+b^3+c^3}{b^3+c^3+d^3}=\dfrac{a}{d}\)
2.Tìm x1; x2 ;x3 ; ... ; x9 biết:
\(\dfrac{x1-1}{9}=\dfrac{x2-2}{8}=\dfrac{x3-3}{7}=...=\dfrac{x9-9}{1}\)
và x1 + x2 + x3 + ... +x9 = 900
Tìm x biết:
a) x-\(\dfrac{2}{3}\)=\(\dfrac{3}{8}\) b) x-\(\dfrac{3}{4}\)=\(\dfrac{13}{10}\):\(\dfrac{26}{5}\) c) \(\dfrac{3}{2}\)-\(\left(x+\dfrac{1}{2}\right)\)=\(\dfrac{4}{5}\) d) |x-2|-1=0
tìm x biết
a) 3/2+7/4x=-5/8
b) |x-3/7|=1/4
Tìm \(x\) trong các tỉ lệ thức sau :
a) \(\left(\dfrac{1}{3}.x\right):\dfrac{2}{3}=1\dfrac{3}{4}:\dfrac{2}{5}\)
b) \(4,5:0,3=2,25:\left(0,1.x\right)\)
c) \(8:\left(\dfrac{1}{4}.x\right)=2:0,02\)
d) \(3:2\dfrac{1}{4}=\dfrac{3}{4}:\left(6.x\right)\)
tính
a) (3^2)^3-(-2^3)^2-(-5^2)^2
b) (-1+3/2/5+1/4).(-4)
tìm x biết
a) x:(-1/3)^3=-1/3b) (x+1/2)^2=1/16
b) (x+1/2)^2=1/16
c) (3x+2)^3=-27
d)27^x:3^x=9
e)16/2^x=2
g)1/2.2^x+4.2^x=9.2^5
1, Thực hiện phép tính :
A = 15/34 + 7/21 + 9/34 - 32/17 + 2/3
B = 114/7 : ( - 3/5) - 198/7 : (-3/5)
C = 25 . ( -1/3 ) + 1/5 - 2.(-1/2)^2 - 1/2
D = ( -2)^3 . ( 3/4 - 0,25 ) : ( 9/4 - 7/6 )
Giúp mình nhé ! cảm ơn các bạn !
