a) x² - 8x = 0
x( x - 8) = 0
x= 0 ......x= 8
b)3x² - 12 = 0
3x² = 12
x² = 12/3
x² = 4
x1= 2.............x2 = - 2
c)3x² -1=0
3x² = 1
x² = 1/3
x = √(1/3)
x1= 0,57..............x2= - 0,57
d)3x² -27x=0
3x( x - 9 ) = 0
3x = 0 ...........x - 9 = 0
x 1= 0..................x2 = 9
e)9x²-225=0
9x² = 225
x² = 225/9
x² = 25
x = √25
x1= 5.....x2= -5
f)16x-4x² =0
4x ( 4 - x )= 0
4x = 0................4-x = 0
x1 =0................x2 = - 4
g)16-x²=0
(4 -x)(4+x) =0....diferencia de cuadrados
4 -x = 0...............4+x = 0
x1 = 4................x2= - 4
h)5x²- x=0
x ( 5x - 1)= 0
x = 0 ..............5x - 1= 0
x1= 0................x2= 1/5
i) - x² - 7x=0
-x ( x + 7) =0....cuidado con los signos
-x =0 ...............x +7= 0
x1= 0 .................x = -7
espero que te sirva, salu2!!!