Question

Tìm số tự nhiên x :

a) 2x + 3.(x+4) - 14 =8

b) x + 2.x + 3.x = 4.x + 16

c) 2.(x+1) + 3.(x + 5) = 0

d) ( x - 3 ).( x - 5 ) = 0

e) (2x - 40). (15 - 3.x) = 0

f) (3.x+6).(28-2.x) + 13 = 13

Answer 1

a)\(2x+3\left(x+4\right)-14=8\)

\(2x+3x+12-14=8\)

\(2x+3x-2=8\)

\(5x-2=8\)

\(5x=8+2\)

\(5x=10\)

\(x=10:5\)

\(x=2\)

Answer 2

b)\(x+2x+3x=4x+16\)

\(x\left(1+2+3\right)=4x+16\)

\(6x-4x=16\)

\(2x=16\)

\(x=16:2\)

\(x=8\)

Answer 3

c)\(2\left(x+1\right)+3\left(x+5\right)=0\)

\(2x+2+3x+15=0\)

\(5x+17=0\)

\(5x=0-17\)

\(5x=-17\)

\(x=-17:5\)

\(x=-\frac{17}{5}\)

Answer 4

d)\(\left(x-3\right).\left(x-5\right)=0\)

\(\hept{\begin{cases}x-3=0\\x-5=0\end{cases}\Rightarrow\hept{\begin{cases}x=3\\x=5\end{cases}}}\)

Vậy \(x\in\left\{3;5\right\}\)