Respostas

2014-08-29T15:57:16-03:00
3a + 9b = 12
8a - 24b = 40

3a + 9b = 12 (-8)
8a - 24b = 40 (3)

-24a -72b = -96
24a - 72b = 120
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/      -144 b= 24
b = -24/144
b = -0,16

3a + 9b = 12
3a + 9.(-0,16) = 12
3a -1,44 =12
3a = 12+1,44
a = 13,44/3
a = 4,48

a² - 9b²
(4,48)² - 9 (-0,16)²
20,07 - 9 . 0,02
20,07 - 0,18
20,25