Question

Câu 17: Tìm x Z , biết:

a) 5 – (10 – x) = 7 b) (4x – 2)(x + 5) = 0

c) 2x – 9 = -8 – 9 d)

e) 5.(3x + 8) –7.(2x + 3) = 16

Answer 1

a) 5 – (10 – x) = 7

<=> 50 - 10 + x = 7

<=> 40 + x = 7

<=> x = -33

b) (4x – 2)(x + 5) = 0

<=> \(\left[{}\begin{matrix}4x-2=0\\x+5=0\end{matrix}\right.\)

<=> \(\left[{}\begin{matrix}x=\frac{1}{2}\\x=-5\end{matrix}\right.\)

c) 2x – 9 = -8 - 9

<=> 2x = -8 - 9 + 9

<=> 2x = -8

<=> x = -4

e) 5.(3x + 8) –7.(2x + 3) = 16

<=> 15x + 40 - 14x - 21 - 16 = 0

<=> x + 3 = 0

<=> x = -3

Answer 2

a) 5-(10-x)=7.
\(\Leftrightarrow\)5-10+x=7.
\(\Leftrightarrow\)x=7+10-5=12.
b) (4x-2)(x+5)=0.
\(\Leftrightarrow\)2(2x-1)(x+5)=0.
\(\Leftrightarrow\)\(\left[{}\begin{matrix}2x-1=0\\x+5=0\end{matrix}\right.\)\(\Leftrightarrow\)\(\left[{}\begin{matrix}x=\frac{1}{2}\\x=-5\end{matrix}\right.\)

c) 2x-9=-8-9.
\(\Leftrightarrow\)2x=-8-9+9.
\(\Leftrightarrow\)2x=-8.
\(\Leftrightarrow\)x=-4.
e)5(3x+8)-7(2x+3)=16.
\(\Leftrightarrow\)15x+40-14x-21=16.
\(\Leftrightarrow\)15x-14x=16+21-40.
\(\Leftrightarrow\)x=-3.