`(15-x)+(x-12)=7-(-5+x)`

`=>15-x+x-12=7+5-x`

`=>3=12-x`

`=>x=12-3`

`=>x=9`

Vậy `x=9`

(15-x)+(x-12) = 7-(-5+x)

<=>15-x+x-12=7+5-x

<=>3=12-x

<=>x=12-3=9

(15-x)+(x-12) = 7-(-5+x)

<=> 15-x +x -12 = 7 +5 -x 

<=> x = 12 +12 -15

<=> x =9

Nam and Phong are best friend, but Minh is Phong neighbour. One day, three of them were in the garden that was very near to their house. Minh is a very shy and clever guy, so he was reading his book and sat on the grass while Nam and Phong were playing basketball. Both of them were a very successful . After a will, Phong threw the ball to Minh and invited him to join both of them. After Minh made up his mind, he joined them immediately. They taught him how to play basketball. And soon, they became best friends, and often plays basketball together.

Ta có: \(x^4-30x^2+31x-30=0\) \(\Rightarrow x^4+x-30x^2+30x-30=0\)

\(\Rightarrow x\left(x^3+1\right)-30\left(x^2-x+1\right)=0\)

\(\Rightarrow x\left(x+1\right)\left(x^2-x+1\right)-30\left(x^2-x+1\right)=0\)

\(\Rightarrow\left(x^2-x+1\right)\left(x^2+x-30\right)=0\)

Xét \(x^2-x+1=\left(x-\frac{1}{2}\right)^2+\frac{3}{4}\ge\frac{3}{4}>0\)

\(\Rightarrow x^2+x-30=0\Rightarrow x^2-5x+6x-30=0\)

\(\Rightarrow\left(x-5\right)\left(x+6\right)=0\Rightarrow\orbr{\begin{cases}x-5=0\\x+6=0\end{cases}\Rightarrow\orbr{\begin{cases}x=5\\x=-6\end{cases}}}\)

Vậy x=5 hoặc x = -6

40 m đường gấp 8 m đường số lần là:

40 : 8 =5(lần)

Sửa 40 m đường thì cần số người là:

3 x 5=15(người)

Đ/S:15 người

Học tốt!

(8x-3)(3x+2)-(4x+7)(x+4) = (2x+1)(5x-1)-33

(24x²-9x+16x-6)-(4x²+7x+16x+28) = (10x²+5x-2x-1)-33

24x²+7x-6-4x²-23x-28 = 10x²+3x-1-33

20x²-16x-34 = 10x²+3x-34

<=> 20x²-16x = 10x²+3x

2x²-19x=0

2x(x-19)=0

=>\(\left[{}\begin{matrix}2x=0\Rightarrow x=0\\x-19=0\Rightarrow x=19\end{matrix}\right.\)

Không chắc lắm :)

3750000 đồng.

Mình đang cần gấp mọi người giải luôn giúp mình nhé. Thanks