Question

Dê o valor numérico:

a)
$4 {x}^{3} - 5x {y}^{2} + {y}^{3}$
Quando x = -2 e y = -4

b)
$\frac{3x - y}{4x + {y}^{2} }$
Quando x =
$- \frac{3}{4}$
e y =
$\frac{1}{2}$

c)
$\frac{a + 5}{ {a}^{2} - 25 }$
Quando a = 5

​

Answer 1

$\sf~a)~4\cdot(-2^3)-5\cdot(-2)\cdot(-4^2)+(-23)\\\\\sf-4\cdot-2^3-5\cdot2^4-2^3\\\\\sf-5\cdot2^3-5\cdot2\cdot2^4\\\\\sf-5\cdot-2^3\cdot(1+2\cdot2)\\\\-5\cdot8\cdot(1+4)\\\\\sf5\cdot8\cdot5\\\\\boxed{-200}~\checkmark\\\\\sf~b)~\frac{3\cdot\left(-\frac{3}{4}\right)-\frac{1}{2}}{4\cdot\left(-\frac{3}{4}\right)+\left(\frac{1}{2}\right)^2}\\\\\\\sf\frac{\frac{-3\cdot3}{~~4}-\frac{1}{2}}{\frac{-4\cdot3}{~~4}+\frac{1}{4}}\\\\\\\sf\frac{-\frac{9}{4}-\frac{1}{2}}{-3+\frac{1}{4}}\\\\\\\frac{-\frac{9+2}{4}}{\frac{-12+1}{4}}\\\\\frac{-\frac{11}{4}}{-\frac{11}{4}}\Rightarrow\boxed{1}~\checkmark\\\\\sf~c)~\frac{5+5}{5^2-25}\Rightarrow\frac{10}{25-25}\Rightarrow\frac{10}{0}~\checkmark$

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