1/3 + 3/35 < x/210 < 4/7 +3/5 +1/3
Ai thông minh giải giúp mình nha. Ahihi.
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\(5\frac{9}{10}:\frac{3}{2}-\left(2\frac{1}{3}x4\frac{1}{2}-2\frac{1}{2}\right):\frac{7}{4}\)
=\(\frac{59}{10}:\frac{3}{2}-\left(\frac{7}{3}x\frac{9}{2}-\frac{5}{2}\right):\frac{7}{4}\)
=\(\frac{118}{30}-\left(\frac{63}{6}-\frac{5}{2}\right)x\frac{4}{7}\)
=\(\frac{118}{30}-\left(\frac{63}{6}-\frac{15}{6}\right)x\frac{4}{7}\)
=\(\frac{118}{30}-8x\frac{4}{7}\)
=\(\frac{118}{30}-\frac{32}{7}\)
sau bn tự tính nha
ta có:
\(1+\frac{1}{4}+\frac{1}{28}+\frac{1}{70}+...+\frac{1}{x\left(x+3\right)}\)=1\(\frac{7}{24}\)\(=\frac{31}{24}\)
\(1+\frac{1}{1.4}+\frac{1}{4.7}+...+\frac{1}{x\left(x+3\right)}=\frac{31}{24}\)
\(3+\frac{3}{1.4}+\frac{3}{4.7}+...+\frac{3}{x\left(x+3\right)}=\frac{31}{3}\)
\(3+1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{x}-\frac{1}{x+3}=\frac{31}{3}\)
\(3+1-\frac{1}{x+3}=\frac{31}{3}\)
\(4-\frac{1}{x+3}=\frac{31}{3}\)
\(\frac{1}{x+3}=4-\frac{31}{3}=\frac{-19}{3}\)
=>ko tìm được x
= \(\dfrac{44}{105}\) < \(\dfrac{x}{210}\) <\(\dfrac{158}{105}\) = \(\dfrac{88}{210}< \dfrac{x}{210}< \dfrac{316}{210}\)
=> x = 89 -> 315
a) \(\frac{x-3}{5}=\frac{4}{9}\)
=> ( x - 3) . 9 = 20
=> 9x - 27 = 20
=> 9x = 47
=> x = \(\frac{47}{9}\)
b) \(\left(x-\frac{1}{4}\right)^2:3^2=81\)
\(\Rightarrow\left(x-\frac{1}{3}\right)^2:9=81\)
\(\Rightarrow\left(x-\frac{1}{4}\right)^2=729\)
\(\Rightarrow x-\frac{1}{4}=27\) hoặc \(x-\frac{1}{4}=-27\)
+) \(x-\frac{1}{4}=27\Rightarrow x=\frac{109}{4}\)
+) \(x-\frac{1}{4}=-27\Rightarrow x=\frac{-107}{4}\)
(X - 1005) x (1 + 3 + 5+ 7 + 9 + 11) = 1989 x 1990 x (70 - 35 x 2)
(X - 1005) x (11 + 1)[(11 - 1) : 2 + 1): 2] = 1989 x 1990 x 0
(X - 1005) x 36 = 0
X - 1005 = 0 : 36
X - 1005 = 0
X = 1005
( x - 1005 ) . ( 1 + 3 + 5 + 7 + 9 + 11 ) = 1989 . 1990 . ( 70 - 35 . 2 )
( x - 1005 ) . 36 = 1989 . 1990 . ( 70 - 70 )
( x - 1005 ) . 36 = 1989 . 1990 . 0
( x - 1005 ) . 36 = 0
x - 1005 = 0
x = 1005
\(\frac{1}{3}+\frac{3}{35}< \frac{x}{210}< \frac{4}{7}+\frac{3}{5}+\frac{1}{3}\)
\(\frac{44}{105}< \frac{x}{210}< \frac{158}{105}\)
\(\frac{88}{210}< \frac{x}{210}< \frac{316}{210}\)
suy ra x = { 89:90;91;............315}
1/3+3/35<x/210<4/7+3/5+1/3
=>44/105<x/210<158/105
=>88/210<x/210<316/210
=>x thuộc {89;90;91;92;...;313;314;315}
k nha bn