Question

resolva as equações do 2° grau, utilizando a fórmula geral:

(a)
$x {}^{2} + 4x - 21 = 0$
(b)
$x {}^{2} + 8x + 16 = 0$

Answer 1

x^2 + 4x - 21 = 0
a = 1; b = 4; c = - 21
∆= b^2-4ac
∆ = 4^2 -4.1.(-21)
∆ = 16+84
∆=100
x = [-b +/- √∆]/2a
x' = [- 4 +/- √100]/2.1

x' = [- 4 + 10]/2 = 6/2 = 3
x" = [- 4 - 10]/2 = - 14/2 = - 7

R.: { 3 ; - 7}

B)
x^2 + 8x + 16= 0
a = 1; b = 8; c = 16
∆ = b^2-4ac
∆ = 8^2 - 4.1.16
∆ = 64 - 64
∆ = 0

x = [ - b +/- √∆]/2a
x' = x" = [ - 8 +/- 0]2.1 = -8/2 = - 4

R.: x = - 4