a)(x - 4)2 - 25= 0
<--> ( x - 4)2 - 52 = 0
<--> ( x - 4 - 5 )( x - 4 + 5 ) = 0
<--> ( x - 4 - 5 ) = 0 <--> x - 9 = 0 <--> x = 9
hoặc
<--> ( x - 4 + 5 ) = 0 <--> x + 1 = 0 <--> x = -1
b)bài này tương tự bài a
\(a,\left(x-4\right)^2-25=0\)
\(\Rightarrow\left(x-4-5\right)\left(x-4+5\right)=0\)
\(\Rightarrow\left(x-9\right)\left(x+1\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x-9=0\\x+1=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=9\\x=-1\end{matrix}\right.\)
\(b,\left(x-3\right)^2-\left(x+1\right)^2=0\)
\(\Rightarrow\left(x-3-x-1\right)\left(x-3+x+1\right)=0\)
\(\Rightarrow-4\left(2x-2\right)=0\)
\(\Rightarrow2\left(x-1\right)=0\)
\(\Rightarrow x-1=0\)
\(\Rightarrow x=1\)
\(c,\left(x^2-4\right)\left(2x+3\right)=\left(x^2-4\right)\left(x-1\right)\)
\(\Rightarrow2x+3=x-1\)
\(\Rightarrow2x-x=-1-3\)
\(\Rightarrow x=-4\)
\(d,\left(3x-7\right)^2-4\left(x+1\right)^2=0\)
\(\Rightarrow\left(3x-7\right)-\left[2\left(x+1\right)\right]^2=0\)
\(\Rightarrow\left(3x-7\right)^2-\left(2x+2\right)^2=0\)
\(\Rightarrow\left(3x-7-2x-2\right)\left(3x-7+2x+2\right)=0\)
\(\Rightarrow\left(x-9\right)\left(5x-5\right)=0\)
\(\Rightarrow5\left(x-9\right)\left(x-1\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x-9=0\\x-1=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=9\\x=1\end{matrix}\right.\)
b, \(\left(x-3\right)^2-\left(x+1\right)^2=0\)
=> \(\left(x-3\right)^2=0\) và \(\left(x+1\right)^2=0\)
=> x-3= 0
=> x= 3
và x+1= 0
=> x=-1
c, \(\left(x^2-4\right)\left(21+3\right)=\left(x^2-4\right)\left(x-1\right)\)
=> \(\dfrac{\left(x^2-4\right)}{\left(x^2-4\right)}=\dfrac{\left(x-1\right)}{21+3}\)
=> \(1=\dfrac{\left(x-1\right)}{21+3}\)
=> x-1= 21+3
=> x-1= 24
=> x= 24+1
=> x=25
