Question

qual o resultado dessa equação x²-4x-21=0 ?

Answer 1

a = 1

b = - 4

c = -21

Δ = (-4 ²) - 4 . 1 . -21

Δ = 16 + 84

Δ = 100

X = - (- 4) +- √100 ÷ 2 . 1

X = 4 + 10 ÷ 2 = 14 ÷ 2 = 7

X = 4 - 10 ÷ 2 = -6 ÷ 2 = -3

S = {7, -3}

Answer 2

x² -4x - 21 = 0

a = 1

b = -4

c = -21

Δ = b² - 4 .a . c

Δ = (-4)² - 4 . 1 . (-21)

Δ = 16 + 84

Δ = 100

$\mathtt{\dfrac{-b+-~\sqrt{\Delta}}{2~.~a}~~=~~\dfrac{-(-4)+-~\sqrt{100}}{2~.~1}~~=~~\dfrac{4+-10}{2}} \\ \\ \\ \mathtt{x' =\dfrac{4+10}{2}~~=~~\dfrac{14}{2}~~=~~7} \\ \\ \\ \mathtt{x'' = \dfrac{4-10}{2}~~=~~-\dfrac{6}{2}~~=~~-3}$

Resposta: S{ - 3 e 7}