Question

Seja
$x {}^{2} + y {}^{2} = 60$
Qual o valor positivo de
$x + y$
,sabendo que
$xy = 20$
?
A》 5
B》10
C》15
D》20
E》25
​

Answer 1

Nenhuma das alternativas apresentadas.

$= (x + y) {}^{2} \\ = x {}^{2} + 2xy + y {}^{2} \\ = x {}^{2} + 2 \: . \: 20 + y {}^{2} \\ = x {}^{2} + 40 + y {}^{2} \\ = x {}^{2} + y {}^{2} + 20 \\ = 60 + 20 \\ \boxed{ = 80 }$

Att. NLE Top Shotta