@Holliwood#:
Đáp án:
a) x1 = $\frac{5-√21}{2}$, x2 = $frac{5+√21}{2}$
b) x1 = $\frac{6-√39}{3}$, x2 = $frac{6+√39}{3}$
Giải thích các bước giải:
a) x²-5x+1=0
⇔ x = $\frac{-(-5)±√(-5)²-4.1.1}{2.1}$
⇔ $\frac{5+√25-4}{2}$
⇔ $\frac{5±√21}{2}$
⇔ $\left \{ {{$\frac{5-√21}{2}$,} \atop {$\frac{5+√21}{2}$}} \right.$
⇒ x1 = $\frac{5-√21}{2}$, x2 = $\frac{5+√21}{2}$
b) 3x²-12x-1=0
⇔ x = $\frac{-(-12)±√(-12)²-4.3.(-1)}{2.3}$
⇔ $\frac{12±√144+124}{6}$
⇔ $\frac{12±√156}{6}$
⇔ $\frac{12±2√39}{6}$
⇔ $\left \{ {{$\frac{12-2√39}{6}$,} \atop {$\frac{12+2√39}{6}$}} \right.$
⇔ $\left \{ {{$\frac{6-√39}{3}$,} \atop {$\frac{6+√39}{2}$}} \right.$
⇒ x1 = $\frac{6-√39}{3}$, x2 = $\frac{6+√39}{3}$
Bn tham khaor nhes!!!!!!!!!!!!!!!!!!!!!!!!!!\
Xin ctlhn aj!!!!!!!!!!!!!
