b) x² + 10xy + 25y²
= x² + 2.x.5y + ( 5y )²
= ( x + 5y )²
c) x² - 2xy + y² - 9z²
= ( x² - 2.x.y + y² ) - ( 3z )²
= ( x - y )² - ( 3z )²
= ( x - y - 3z )( x - y + 3z )
2 . Tìm x :
a) 3( x - 5 ) + x + 5 = 0
⇔ 3x - 15 + x + 5 = 0
⇔ 4x - 10 = 0
⇔ 2x - 5 = 0
⇔ 2x = 5
⇔ x = $\frac{5}{2}$
Vậy x = $\frac{5}{2}$
b) 7x( x - 2 ) = x - 2
⇔ 7x( x - 2 ) - ( x - 2 ) = 0
⇔ ( x - 2 )( 7x - 1 ) = 0
⇔ \(\left[ \begin{array}{l}x-2=0\\7x-1=0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=2\\x=\frac{1}{7} \end{array} \right.\)
~CHÚC BẠN HỌC TỐT~
