Question

Use a formula quadratica para resolver a equação !
-7x²+ 2x +9=0

Answer 1

a = -7
b = 2
c = 9

$\Delta~=b^{2}-4.a.c \\ \Delta~=2^{2}-4.(-7).9 \\ \Delta~=4+252 \\ \Delta~=256 \\ \\ x= \frac{-b+/- \sqrt{\Delta~}}{2a} \\ x= \frac{-2+/- \sqrt{256}}{2.(-7)} \\ x= \frac{-2+/-16}{-14} \\ \\ x'= \frac{-2+16}{-14} \\ x'=-1 \\ \\ x''= \frac{-2-16}{-14}= \frac{-18}{-14}:2= \frac{9}{7}$