Question

a) A³ - 5a ( para a= -2)

b) x² - 2y ( para x= -3 e y = 5)

c) 3 a² + b² ( para a= - a = - 2 e b = -7)

d) 5 a² + 3 ab ( para a= - 3 e b = 4)

e) a² + 4a ( para a = 2/3)​

Answer 1

Para determinar o valor númerico, substitua as letras pelos números dados

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$\underbrace{Veja:}$

a) Para a = -2

$\Rightarrow~~a^3-5a$

$\Rightarrow~~(-2)^3-5.(-2)$

$\Rightarrow~~-8-(-10)$

$\Rightarrow~~-8+10$

$\therefore~~\boxed{2}$

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b) Para x = -3 e y = 5

$\Rightarrow~~x^2-2y$

$\Rightarrow~~(-3)^2-2.(5)$

$\Rightarrow~~9-10$

$\therefore~~\boxed{-1}$

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c) Para a = -2 e b = -7

$\Rightarrow~~3a^2+b^2$

$\Rightarrow~~3.(-2)^2+(-7)^2$

$\Rightarrow~~3.4+49$

$\Rightarrow~~12+49$

$\therefore~~\boxed{61}$

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d) Para a = -3 e b = 4

$\Rightarrow~~5a^2+3ab$

$\Rightarrow~~5.(-3)^2+3.(-3).(4)$

$\Rightarrow~~5.9+(-36)$

$\Rightarrow~~45-36$

$\therefore~~\boxed{9}$

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e) Para a = 2/3

$\Rightarrow~~a^2+4a$

$\Rightarrow~~\bigg(\dfrac{2}{3}\bigg)^2+4.\bigg(\dfrac{2}{3}\bigg)$

$\Rightarrow~~\dfrac{4}{9}+\dfrac{8}{3}$

MMC (9 , 3) = 9

$\Rightarrow~~\dfrac{9\div9\cdot4}{9}+\dfrac{9\div3\cdot8}{9}$

$\Rightarrow~~\dfrac{4}{9}+\dfrac{24}{9}$

$\Rightarrow~~\dfrac{4+24}{9}$

$\therefore~~\boxed{\dfrac{28}{9}}$