Question

tìm x, biết:

a) (x+7)²-x.(x-3)=12

b) (x+1)²-(x-2).(x+2)=0

Answer 1

a) x^2 + 14x + 49 - x^2 + 3x = 12
<=> 17x = -37
<=> x = -37/17
b) x^2 + 2x +1 - x^2 + 4 = 0
<=> 2x = -5
<=> x = -5/2  

Answer 2

a) \(\left(x+7\right)^2-x\left(x-3\right)=12\)

\(\Leftrightarrow x^2+14x+49-x^2+3x=12\)

\(\Leftrightarrow17x=-37\)

\(\Leftrightarrow x=\frac{-37}{17}\)

Vậy x = -37/17

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

\(\Leftrightarrow x^2+2x+1-\left(x^2-4\right)=0\)

\(\Leftrightarrow x^2+2x+1-x^2+4=0\)

\(\Leftrightarrow2x=-5\)

\(\Leftrightarrow x=\frac{-5}{2}\)

Vậy x = -5/2

Answer 3

a) \(\left(x+7\right)^2-x\left(x-3\right)=12\)

\(x^2+14x+49-x^2+3x=12\)

\(17x=-37\)

\(\Rightarrow x=\frac{-37}{17}\)

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

Áp dụng hằng đẳng thức :

\(\Rightarrow x^2+2x.1^2+1^2-\left(x^2+4\right)=0\)

\(\Rightarrow x^2+2x+1-x^2+4=0\)

\(\Rightarrow2x=-5\)

\(\Leftrightarrow x=\frac{-5}{2}\)

_Chúc bạn học tốt _