Question

me ajudem nas equaçoes do 2 grau incompletas
a) x ²+7x=0
b) -3x ²+9x=0
c)2x ²+3x=0
d)x ²+9x=0
e) (y+5). (y-1)=2y-5
f)2x ²-18=0
g)-5x ²+20=0
h)9a ²=25
i) (b+4).(b-4)=0
j)5y ²-3y-2+y ²-2
k)x ²+9x+20=9x

Answer 1

Olár!

a) x² + 7x = 0
x (x + 7) = 0
x = 0 ou
x +7 = 0
x = -7

b) -3x² + 9x = 0
x (-3x + 9) = 0
x = 0 ou
-3x + 9 = 0
x = 3

c) 2x² + 3x= 0
x (2x + 3) = 0
x = 0 ou
2x + 3 = 0
x = -3/2

d) x² + 9x = 0
x (x + 9) = 0
x = 0 ou
x + 9 = 0
x = -9

e) (y + 5)(y - 1) = 2y - 5
y² - y + 5y - 5 = 2y - 5
y² + 2y = 0
y (y + 2) = 0
y = 0 ou
y + 2 = 0
y = -2

f) 2x² - 18 = 0
2x² = 18
x = 3

g) -5x² + 20 = 0
5x² = 20
x = 2

h) 9a² = 25
a = 5/3

i) (b+4)(b-4) = 0
b² - 16 = 0
b² = 16
b = 4

j) 5y² - 3y - 2 + y² - 2 = 0
6y² - 3y - 4 = 0
Δ = 9 - 4*6*(-4)
Δ = 105
x = 3 +/- √105/12

x' = 3 + √105/12
x'' = 3 - √105/12

k) x² + 9x + 20 = 9x
x² + 20 = 0
x² = -20
x = √-20