Question

Tìm x biết: 

x² - 17x = 60.

Answer 1

\(x^2-17x=60\)

\(\Rightarrow x^2-17x-60=0\)

=> (x - 20)(x + 3) = 0

=> x = 20 hoặc x = -3

Answer 2

\(\Leftrightarrow\)\(x^2-17x-60=0\)

\(\Leftrightarrow\)\(x^2-20x+3x-60=0\)

\(\Leftrightarrow\)\(x(x-20)+3(x-20)=0\)

\(\Leftrightarrow\)\((x+3)(x-20)=0\)

\(\Leftrightarrow\)\(\left[\begin{array}{} x=-3\\ x=20 \end{array} \right.\)

Answer 3

\(\left(x^2-2.x.\left(\dfrac{17}{2}\right)^2\right)-\left(\left(\dfrac{17}{2}\right)^2\right)=60\)

\(\left(x-\dfrac{17}{2}\right)^2=60+\dfrac{289}{4}=\left(\dfrac{23}{2}\right)^2\)

TH1:x-17/2=23/2⇒x=63/4

TH2:x-17/2=-23/2⇒x=-29/4