a. 2(x+6)-7=5(x-1)

b.(x+5)(2x-1)+x^2-25=0

Đáp án+Giải thích các bước giải:

$a.$  $2$$($$x$$+$$6$$)$$-$$7$$=$$5$$($$x$$-$$1$$)$

  $\Longleftrightarrow$ $2x$$+$$12$$-$$7$$=$$5x$$-$$5$

$\Longleftrightarrow$   $2x$$-$$5x$$=$$7$$-$$5$$-$$12$

  $\Longleftrightarrow$$-$$3x$$=$ -$$10$

$\Longleftrightarrow$$x$$=$$\dfrac{-10}{-3}$ 

$\Longleftrightarrow$ $x$$=$$\dfrac{10}{3}$ 

$b$. $($ $x$ $+$ $5$ $)$ $($ $2x$ $-$ $1$ $)$ $+$$x^2$ $-$ $25$ $=$ $0$

$\Longleftrightarrow$$2x^2$$-$$x$$+$$10x$$-$$5$$+$$x^2$$-$$25$$=$$0$

$\Longleftrightarrow$$2x^2$$+$$x^2$$-$$x$$+$$10x$$-$$5$$-$$25$$=$$0$

$\Longleftrightarrow$$3x^2$$+$$9x$$-$$30$$=$$0$        $($$casio$$)$

$\Longleftrightarrow$$\left[\begin{matrix} x=2\\ x=-5\end{matrix}\right.$