Temos que:
F(x) = ax + b
F(-1) = a*(-1) + b
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7 = -a + b
b= 7 + a
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F(2) = 2a + b
1 = 2a + b
1 = 2a + 7 + a
-6 = 3a
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a= - 2
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b = 7 + a
b= 7 + (-2)
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b= 5
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Portanto a função fica:
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f(x) = -2x + 5
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