Question

a-) (7a+1) x (7a-1)=
b-) (2+9x)²=
c-) (6x-y)² =

Answer 1

a)
(7a + 1).(7a - 1) 
= 7a.7a - 1.7a + 1.7a + 1.(-1) 
= 49a² - 7a + 7a - 1
= 49a² - 1

b)
(2 + 9x)²
= (2 + 9x) . ( 2 + 9x)
= 2.2 + 2.9x + 2.9x + 9x.9x
= 4 + 18x + 18x + 81x²
= 81x² + 36x + 4

c) 
= (6x - y)²  
= (6x - y).(6x - y) =  36x² - 2.6x.y + y²
= 6x.6x - y.6x - y.6x - y.(-y)
= 36x² - 6xy - 6xy + y²

= 36x² - 12xy + y²

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SISTEMAS - COMPLEMENTAR:
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a)
3x – y = 18
x + y = 40

x = 40 - y

3x - y = 18
3(40 - y) - y = 18
120 - 3y - y = 18
- 4y + 120 = 18
- 4y = 18 - 120
 - 4y = - 102 (-1)
4y = 102
y = 102/4
y = 102 (:2) =  51
        4  (:2)      2

y = 51
      2

x = 40 - y
x = 40 - 51
             2

2x = 80 - 51
2x = 29
x = 29
       2
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b)
2x + y = -3
x - 3y = - 26

2x + y = - 3
y = - 3 - 2x

x - 3y = - 26
x - 3(- 3 - 2x) = - 26
x + 9 + 6x = - 26
7x + 9 = - 26
7x = - 26 - 9
7x = - 35
x = - 35/7
x = - 5 

2x + y = - 3
2.(-5) + y = - 3
- 10 + y = - 3
y = - 3 + 10
y = 7