Đáp án + Giải thích các bước giải:
a) $\text{Ta có}$
$\text{( x - 4 )² - x² }$
$\text{=> ( x - 4 -x ) . ( x - 4 + x ) = 3}$
$\text{=> - 4 . ( 2x - 4 ) = 3 }$
$\text{=>- 8x + 16 = 3}$
$\text{=>- 8x = - 13}$
$\text{=> x = $\frac{13}{8}$ }$
b) $\text{Ta có :}$
$\text{( x + 2 )² - ( 3 + x )²= 20}$
$\text{=> ( x + 2 - 3 - x ) . ( x + 2 + 3 + x ) = 20}$
$\text{=> - 1. ( 2x + 5 ) = 20}$
$\text{=> - 2x - 5 = 20}$
$\text{=>- 2x = 25}$
$\text{=> x = $\frac{-25}{2}$ }$
c) $\text{Ta có :}$
$\text{x² + 20x + 100 = 0}$
$\text{=> x² + 2.10x + 10² = 0}$
$\text{=>( x + 10)²= 0}$
$\text{=> x + 10 = 0 => x = - 10}$
d) $\text{4x² - 36x + 81 = 0}$
$\text{=> ( 2x )² - 2.2.9x + 9² = 0}$
$\text{=> (2x + 9)² = 0}$
$\text{=> 2x + 9 = 0 }$
$\text{=> x = $\frac{-9}{2}$ }$
$\text{Gửi bạn nha , xin hay nhất nha <3}$
