Question

Answer 1

Bài 3:
a.

$x^2-\frac{1}{49}=0$

$\Leftrightarrow (x-\frac{1}{7})(x+\frac{1}{7})=0$

$\Leftrightarrow x-\frac{1}{7}=0$ hoặc $x+\frac{1}{7}=0$

$\Rightarrow x=\pm \frac{1}{7}$

b.

$(5x+20)-x^2-4x=0$

$\Leftrightarrow 5(x+4)-x(x+4)=0$

$\Leftrightarrow (x+4)(5-x)=0$

$\Rightarrow x+4=0$ hoặc $5-x=0$

$\Leftrightarrow x=-4$ hoặc $x=5$

c.

$(5x-1)^2-196=0$

$\Leftrightarrow (5x-1)^2-14^2=0$

$\Leftrightarrow (5x-1-14)(5x-1+14)=0$

$\Leftrightarrow (5x-15)(5x+13)=0$

$\Rightarrow 5x-15=0$ hoặc $5x+13=0$

$\Leftrightarrow x=3$ hoặc $x=\frac{-13}{5}$