Question

2. Tìm số nguyên x, biết:

a) x+5+2.x=17

b) x-11=2.x+4

c) (3-x).(x+5)=0

d) (2.x+2).(x-19)=0

e) (x+2)3=(-125)

f) |x-3|=4

g) 2.|7-x|=16

h) 12-2.|x-10|=(-18)

Answer 1

a) x+5+2.x=17

x.1+2x=17-5

x.(2+1)=12

x.3=12

x=12:3

x=4

vay x = 4

c) (3-x).(x+5)=0

\(\Rightarrow\left[{}\begin{matrix}3-x=0\\x+5=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=3-0\\x=0-5\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=3\\x=-5\end{matrix}\right.\)

vay x \(\in\left\{3:-5\right\}\)

d) (2.x+2).(x-19)=0

\(\Rightarrow\left[{}\begin{matrix}2x+2=0\\x-19=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}2x=0-2\\x=0+19\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}2x=-2\\x=19\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-2:2\\x=19\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-1\\x=19\end{matrix}\right.\)

vay x \(\in\left\{-1;19\right\}\)

e) (x+2)3=(-125)

x+2=-125:3( loai )

vay x ko co gia tri nao thoa man

f) |x-3|=4

\(\Rightarrow\left[{}\begin{matrix}x-3=4\\x-3=-4\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=4+3\\x=-4+3\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=7\\x=-1\end{matrix}\right.\)

vay x\(\in\left\{7;-1\right\}\)

g) 2.|7-x|=16

\(\)/7-x/=16:2

/7-x/=8

\(\Rightarrow\left[{}\begin{matrix}7-x=-8\\7-x=8\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-8+7\\x=8+7\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-1\\x=15\end{matrix}\right.\)

vay \(x\in\left\{-1;15\right\}\)

h) 12-2.|x-10|=(-18)

2/x-10/=-18+12

2/x-10/=-6

/x-10/=-6:2

/x-10/=-3

\(\Rightarrow\left[{}\begin{matrix}x-10=3\\x-10=-3\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=3-10\\x=-3+10\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-7\\x=7\end{matrix}\right.\)

vay \(x\in\left\{-7;7\right\}\)

Answer 2

sorry ban vi mik ko lam dc phan b mong ban thong cam

Answer 3

mik xin thay Trần Ngoc an làm câu b

x-11=2x+4

=> x-11-4 = 2x

=> x-15 = 2x

=> x-15 = x+x

=> x-15 = x - (-x)

=> 15= -x

=> x = -15

Answer 4

@Vũ Ngọc Diệp ơi, mk lm câu b nhưng ko giống cách của bn @nguyễn huy hoàng (tag hộ) nhé!!!

b) x-11 =2.x+4

-11-4= 2x - x

-11+(-4)= x

-15 = x

=> x = -15

Answer 5

a, x+5 + 2x = 17

3x + 5 = 17

3x = 12

x = 4 ( thỏa mãn )

b, x - 11 = 2x + 4

x - 2x = 4 + 11

-x = 15

x = -15 ( thỏa mãn )

c, (3 - x)(x + 5) = 0

\(\Rightarrow\left[{}\begin{matrix}3-x=0\\x+5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\left(thỏamãn\right)\\x=-5\left(thỏamãn\right)\end{matrix}\right.\)

d,(2x + 2)(x - 19) = 0

\(\Rightarrow\left[{}\begin{matrix}2x+2=0\\x-19=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-1\left(thỏamãn\right)\\x=19\left(thỏamãn\right)\end{matrix}\right.\)

e, (x + 2)3 = -125

x +2 = \(\frac{-125}{3}\)

x = \(\frac{-131}{3}\left(loại\right)\)

f, |x - 3| = 4

TH1: x - 3 = 4

x = 7 (thỏa mãn)

TH2: x - 3 = -4

x = -1 (thỏa mãn)

g, 2.|7 - x| = 16

|7 - x| = 8

TH1: 7 - x = 8

x = -1 (thỏa mãn)

TH2: 7 - x = -8

x = 15 (thỏa mãn)

h, 12 - 2.|x - 10| = -18

-2.|x - 10| = -30

|x - 10| = 15

TH1: x - 10 = 15

x = 25 (thỏa mãn)

TH2: x - 10 = -15

x = -5 (thỏa mãn)

Chúc bạn học tốt !