Question

X²-81=0

X²-x=0

X²-3=78

16x²=81

X²-12=0

Answer 1

Olá,

x² - 81 = 0
x² = 81
x = +-√81
x = +- 9
S = {-9, 9)

x²-x=0
x(x-1) = 0
x = 0
x -1 = 0
x = 1
S = {0,1}

x²-3=78
x² = 78 + 3
x² = 81
x = +-√81
x = +-9
S = {-9, 9}

16x²=81
x² = 81/16
x = √81/√16
x = +-9/4
S = {-9/4, 9/4}

x²-12=0
x² = 12
x = √12
x = √2²*3
x = +-2√3
S = {-2√3, 2√3}

Bons estudos ;)

Answer 2

Boa tarde Rafaella

a) 

x² - 81 = 0
x² = 81
x1 = -9
x2 = +9

b) 

x² - x = 0
x*(x - 1) = 0
x1 = 0
x2 = 1

c) 

x² - 3 = 78
x² = 78 + 3 = 81
x1 = -9
x2 = +9

d) 

16x² = 81
x² = 81/16 
x1 = -9/4
x2 = +9/4

e)

x² - 12 = 0
x² = 12 = 3*4
x1 = -2√3
x2 = +2√3