Question

Responda com contas completas:

$3x + y = 20 \\ x + 4y = 3$

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$4a + 2b = 8 \\ 5a - 7b = 29$
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Answer 1

a)

$3x + y = 20 \\ x + 4y = 3 \times ( - 3) \\ \: \: 3x + y = 20 \\ - 3x - 12y = - 9 \\ - 11y = 11 \times ( - 1)$

$11y = - 11 \\ y = - \frac{11}{11} = - 1$

$x + 4y = 3 \\ x = 3 - 4y \\ x = 3 - 4.( - 1) \\ x = 3 + 4 = 7$

S={7,-1}

b)

$4a + 2b = 8 \times (7) \\ 5a - 7b = 29 \times (2) \\ 28a + 14b = 56 \\ 5a - 14b = 58 \\ 33a = 114$

$a = \frac{114 \div 3}{33 \div 3} = \frac{38}{11}$

$4a + 2b = 8 (\div 2) \\ 2a + b = 4 \\ b = 4 - 2a \\ b = 4 - 2. \frac{38}{11}$

$b = 4 - \frac{76}{11} = \frac{44 - 76}{11} \\ b = - \frac{32}{11}$