Question

Rezolvati in R ecuatiile x la puterea 2 -8x-9=0

Answer 1

$\displaystyle x ^ 2 -8x-9=0 \\ \Delta= b^2-4ac\\ \Delta=(-8)^2-4 \cdot 1 \cdot (-9) = 100 \\ \\ \boxed{X_{1,2}= \frac{-b\pm \sqrt{\Delta} }{2a} } \\ \\ \\ X1= \frac{8-10}{2}= \frac{-2}{2}=-1 \\ \\ \\ X2= \frac{8+10}{2}= \frac{18}{2}=9$

Answer 2

x²-8x-9=0

x²-9x+x-9=0

x(x-9)+x-9=0

(x+1)(x-9)=0

x+1=0 sau x-9=0
x=-1 sau x=9