Question

Tìm x

a, 580 :( x -24 ) =329 -150 : 2

b, 7 (x-1 ) +35= 25 + 279 :9

c,4 ( 2x+ 7 ) -3 (3x -2 ) =24

d,( x-1 ) (x-2) =3(x-1)

e,( x+ 3 ) + ( x+7 ) + ( x + 11 ) + ........+ ( x+ 79 ) =860

Answer 1

a, ĐK: \(x\ne24\)

580 :( x -24 ) =329 -150 : 2

<=> 580 :( x -24 ) = 329 - 75

<=> 580 :( x -24 ) = 254

<=> x - 24 = \(\frac{290}{127}\)

<=> x = \(\frac{3338}{127}\left(TM\right)\)

Vậy \(x=\frac{3338}{127}\)

b, 7 (x-1 ) +35= 25 + 279 :9

<=> 7x - 7 + 35 = 25 + 31

<=> 7x +28 = 56

<=> 7x = 28

<=> x = 4

Vậy x =4

c,4 ( 2x+ 7 ) -3 (3x -2 ) =24

<=> 8x + 28 - 9x + 6 = 24

<=> 34 - x = 24

<=> x = 10

Vậy x = 10

d,( x-1 ) (x-2) =3(x-1)

<=> ( x-1 ) (x-2) - 3(x-1) = 0

<=> (x- 1)(x - 2 - 3) = 0

<=> (x -1)(x - 5) = 0

<=> \(\left[{}\begin{matrix}x-1=0\\x-5=0\end{matrix}\right.\) <=> \(\left[{}\begin{matrix}x=1\\x=5\end{matrix}\right.\)

Vậy x ={1; 5}

Answer 2

e, (x + 3) + (x + 7) + (x + 11) + ... + (x + 79) = 860

x + 3 + x + 7 + x + 11 + ... + x + 79 = 860

Có tất cả: (79 - 3) : 4 + 1 = 20 số hạng \(\Rightarrow\) có 20x

hay x + 3 + x + 7 + x + 11 + ... + x + 79 = 860

\(\Rightarrow\) 20x + (3 + 7 + ... + 79) = 860

3 + 7 + ... + 79 = (79 + 3) x 20 : 2 = 820

\(\Rightarrow\) 20x + (3 + 7 + ... + 79) = 860

\(\Rightarrow\) 20x + 820 = 860

\(\Rightarrow\) 20x = 40

\(\Rightarrow\) x = 2

Vậy x = 2

Chúc bn học tốt!