Tìm x, biết:
a ) | x | = 1 4 + 4 7 ; b ) | x − 1 | = 7 2 + − 4 − 3 ;
c ) x − 2 3 = − − 1 5 + 3 4 ; d ) x − 3 4 = 1 5 + 1 7 − 1 14 .
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a) Ta có:
1; 4; 7;...; 100 có (100 - 1) : 3 + 1 = 34 (số)
1 + 4 + 7+ ... + 100 = (100 + 1) × 34 : 2
= 101 × 17
(1 + 4 + 7 + ... + 100) : a = 17
101 × 17 : a = 17
a = 101 × 17 : 17
a = 100
b) (X - 1/2) × 5/3 = 7/4 - 1/2
(X - 1/2) × 5/3 = 5/4
X - 1/2 = 5/4 : 5/3
X - 1/2 = 3/4
X = 3/4 + 1/2
X = 5/4
a) (1 + 4 + 7 +...+ 100) : a = 17
1717 : a = 17
a = 101
b) \(\left(x-\dfrac{1}{2}\right)\times\dfrac{5}{3}=\dfrac{7}{4}-\dfrac{1}{2}\)
\(\left(x-\dfrac{1}{2}\right)\times\dfrac{5}{3}=\dfrac{10}{8}\)
\(\left(x-\dfrac{1}{2}\right)=\dfrac{10}{8}\div\dfrac{5}{3}\)
\(\left(x-\dfrac{1}{2}\right)=\dfrac{10}{8}\times\dfrac{3}{5}\)
\(\left(x-\dfrac{1}{2}\right)=\dfrac{3}{4}\)
\(x-\dfrac{1}{2}=\dfrac{3}{4}\)
\(x=\dfrac{3}{4}+\dfrac{1}{2}\)
\(x=\dfrac{5}{4}\)
a, ( 1 + 4 + 7 + .........+ 100 ) : a = 17
( ( 100 - 1 ) : 3 + 1 ) : a = 17
( 99 : 3 + 1 ) : a = 17
34 : a = 17
34:17
2
vậy a = 2
b, ( x - 1/2 ) x 5/3 = 7/4 - 1/2
( x - 1/2 ) x 5/3 =5/4
x - 1/2 = 5/4 : 5/3
x - 1/2 = 3/4
x = 1/2 + 3/4
x= 5/4
vậy x = 5/4
hok tốt
A , ( 1 + 4 + 7 + ... + 100 ) : a = 17
=> 1 + 4 + 7 + .. + 100 = 17 x a
khoảng cách giữa mỗi số là :
4 - 1 = 3
dãy số trên có số số hạng là :
( 100 - 1 ) : 3 + 1 = 34 ( số hạng )
( 100 + 1 ) x 34 : 2 = 17 x a
101 x 17 = 17 x a
=> a = 101
B , ( X - 1/2 ) x 5/3 = 7/4 - 1/2
X - 1/2 = 5/4 : 5/3
X - 1/2 = 3/4
X = 3/4 + 1/2
X = 5/4
(x-1/2).5/3=7/4-1/2
(x-1/2).5/3=5/4
x-1/2=5/4:5/3
x=3/4+1/2
x=5/4
(x-4/3).7/4=5-7/6
(x+4/3).7/4=23/6
x+4/3=23/6:7/4
x+4/3=46/21
x=46/21-4/3
x=6/7
a, x+4/7=7/4-1/4
x + 4/7 = 6/4
x = 6/4 - 4/7
x = 26/28
b, 9/2+(x-3/4)=25/4
x - 3/4 = 25/4 - 9/2
x - 3/4 = 7/4
x = 7/4 + 3/4
x = 10/4
a, x+4/7=7/4-1/4
x+4/7= 3/2
x = 3/2-4/7= 13/14
b,9/2+(x-3/4)=25/4
x-3/4 = 25/4 - 9/2 = 7/4
x= 7/4 + 3/4 = 5/2
a. \(\dfrac{8}{7}-\dfrac{1}{7}:\left(\dfrac{x}{3}-2\right)=-1\)
\(-\dfrac{1}{7}:\left(\dfrac{x}{3}-2\right)=\dfrac{15}{7}\)
\(\dfrac{x}{3}-2=\dfrac{-1}{15}\)
\(\dfrac{x}{3}=\dfrac{29}{15}\)
\(x=5,8\)
b. \(\dfrac{5}{8}+\dfrac{1}{4}\left(2x-1\right)=\dfrac{5}{4}\)
\(\dfrac{1}{4}\left(2x-1\right)=\dfrac{5}{8}\)
\(2x-1=\dfrac{5}{2}\)
\(2x=\dfrac{7}{2}\)
\(x=\dfrac{7}{4}\)
Lớp 4?
a) \(\dfrac{x+1}{4}=\dfrac{36}{x+1}\)
\(\Rightarrow\left(x+1\right)^2=144\)
\(\Rightarrow\left[{}\begin{matrix}x+1=12\\x+1=-12\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=11\\x=-13\end{matrix}\right.\)
Vậy: \(x\in\left\{11;-13\right\}\)
b) \(\dfrac{x}{7}=\dfrac{55x-4}{28}\)
\(\Rightarrow4x=55x-4\)
\(\Rightarrow-51x=-4\)
\(\Rightarrow x=\dfrac{4}{51}\)
Vậy: \(x=\dfrac{4}{51}\)
a) \(\dfrac{x + 1}{4} = \dfrac{36}{x + 1} \)
\(\Rightarrow\) \(( x + 1 )( x + 1 ) = 36 . 4 \)
\(\Rightarrow ( x + 1 )^2 = 144 \)
\(\Rightarrow ( x + 1 )^2 = 12^2 = ( -12 )^2 \)
\(\Rightarrow\) \(x + 1 ∈ \) { \(12 ; -12 \) }
\(\Rightarrow \) \(x \) \(∈ \) { \(11 ; -13 \) }
Vậy \(x ∈ \) { \(11 ; -13 \) }
a) 4/7 x X = 1/5 + 2/3
=> 4/7 x X = 3/15 + 10/15
=> 4/7 x X = 13/15
=> X = 13/15 : 4/7
=> X = 13/15 x 4/7 = 52/105
a ) 4 / 7 x X = 1 / 5 + 2 / 3
= > 4 / 7 x X = 3 / 1 5 + 1 0 / 1 5
= > 4 / 7 x X = 1 3 / 1 5
= > X = 1 3 / 1 5 : 4 / 7
= > X = 1 3 / 1 5 x 4 / 7
= 5 2 / 1 0 5
a ) x ∈ ± 23 28 . b ) x ∈ − 23 6 ; 35 6 . c ) x ∈ − 17 60 ; 97 60 . d ) x ∈ 67 140 ; 143 140 .