x2−4x+4=25
⇒(x2−4x+4)−25=0
⇒(x−2)2−52=0
⇒(x−2−5)(x−2+5)=0
⇒(x−7)(x+3)=0
⇒[x−7=0x+3=0⇒[x=7x=−3
Vậy x = 7 hoặc x= -3
x2-4x+4=25
<=> x2-2.2x+22=25
<=> (x-2)2=25
<=> x-2=5
<=> x=7
\(x^2-4x+4=25\)
\(\Rightarrow\left(x^2-4x+4\right)-25=0\)
\(\Rightarrow\left(x-2\right)^2-5^2=0\)
\(\Rightarrow\left(x-2-5\right)\left(x-2+5\right)=0\)
\(\Rightarrow\left(x-7\right)\left(x+3\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x-7=0\\x+3=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=7\\x=-3\end{matrix}\right.\)
Vậy x = 7 hoặc x= -3
Lớp 8 à quất luôn pt bậc 2 cho thầy cô sợ =))
\(x^2-4x+4=25\)
\(\Leftrightarrow x^2-4x-21=0\)
\(\Delta=b^2-4ac=\left(-4\right)^2-4.\left(-12\right)=100\)
\(\Rightarrow\sqrt{\Delta}=10\)
\(\Rightarrow x_1=\frac{-b+\sqrt{\Delta}}{2a}=\frac{4+10}{2}=7\)
\(\Rightarrow x_2=\frac{-b-\sqrt{\Delta}}{2a}=\frac{4-10}{2}=-3\)
:))