a/ Ta có : \(49.x^2-4=0\)
\(\Rightarrow49x^2=4\)
\(\Rightarrow x^2=\frac{4}{49}\Rightarrow\orbr{\begin{cases}x=\frac{-2}{7}\\x=\frac{2}{7}\end{cases}}\)
b/ \(\left(x+3\right)^2-\left(x+2\right)\left(x-2\right)=11\)
\(\left(x+3\right)\left(x+3\right)-\left(x+2\right)\left(x-2\right)=11\)
\(\Rightarrow\left(x^2+2.3.x+3^2\right)-\left(x^2-2^2\right)=11\)
\(\Rightarrow x^2+6x+9-x^2+4=11\)
\(\Rightarrow6x+13=11\)
\(\Rightarrow6x=11-13\)
\(\Rightarrow x=\frac{-2}{6}=\frac{-1}{3}\)
c/ \(\left(2x+1\right)^2-\left(x-3\right)^2-3\left(x+5\right)\left(x-5\right)=5\)
\(\Rightarrow\left(2x+1\right)\left(2x+1\right)-\left(x-3\right)\left(x-3\right)-3\left[\left(x+5\right)\left(x-5\right)\right]=5\)
\(\Rightarrow\left(4x^2+2.2x+1\right)-\left(x^2-2.3x+9\right)-3\left(x^2-25\right)\)\(=5\)
\(\Rightarrow\left(4x^2+4x+1\right)-\left(x^2-6x+9\right)-\left(3x^2-75\right)=5\)
\(\Rightarrow4x^2+4x+1-x^2+6x-9-3x^2+75=5\)
\(\Rightarrow\left(4x^2-x^2-3x^2\right)+\left(4x+6x\right)+\left(1-9+75\right)=5\)
\(\Rightarrow10x+67=5\)
\(\Rightarrow10x=5-67=-62\)
\(\Rightarrow x=\frac{-62}{10}=\frac{-31}{5}\)
d/ \(\left(3x+1\right)\left(3x-1\right)=8\)
\(\Rightarrow9x^2-1=8\)
\(\Rightarrow9x^2=8+1=9\)
\(\Rightarrow x^2=\frac{9}{9}=1\Leftrightarrow\orbr{\begin{cases}x=-1\\x=1\end{cases}}\)
Ai đó bấm hộ mình cái nút đúng đi!
Ta có : 49x2 - 4 = 0
=> 49x2 = 4
=> x2 = 196
=> x2 = 142 ; (-14)2
=> x = 14 ; -14
a) 49 . x2 - 4 = 0
49 . x2 = 4
7 2 . x2 = 22
(7 . x)2 = 22
7 . x = 2
x = 2 : 7
x = \(\frac{2}{7}\)
