Question

Tìm x:

a) 5x-7=x+57

b) x+3x-12=28

c) x(x-3)=0.

d)(2x-4)(x+1)=0 

e) 1+2+3+4+.......+x=120

Answer 1

a) <=>5x-x=57+7

<=> 4x=64

<=> x=16

b) <=>4x=28+12

<=> x=40/4

<=>10

c) th1 x=0

th2 x-3=0

<=>x=3

d) th1 2x-4=0

<=> x=2

th2 x+1=0

<=> x=-1

câu e mình ko biết làm hihi 

Answer 2

a, 5x - 7 = x + 57

5x - x = 57 + 7

4x = 64

x = 64 : 4

x = 16

b, x + 3x - 12 = 28

4x = 28 + 12

4x = 40

x = 10

c, x(x-3) = 0

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

d, (2x-4)(x+1)=0

\(\Rightarrow\orbr{\begin{cases}2x-4=0\\x+1=0\end{cases}\Rightarrow\orbr{\begin{cases}x=2\\x=-1\end{cases}}}\)

e, 1+2+...+x=120

=> \(\frac{x\left(x+1\right)}{2}=120\)

=> x(x+1) = 120.2

=>x(x+1) = 240

=> x(x+1) = 15.16

=> x=16