How do you solve the following system: $x + 8y = 15 , x + 4y = -2$ ?

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Answer 1 · 2015-12-18T15:28:18

$x = -19$
$y = 17/4$

You can already say with the 2nd equation that $x = -2 - 4y$ .

You replace x by its new expression in the 1st line :

$x + 8y = 15 iff -2 - 4y + 8y = 15 iff 4y = 17 iff y = 17/4$

You now replace y by its value in the second equation !

$x = -2 - 4y iff x = -2 - 17 iff x = -19$

How do you solve the following system: x + 8y = 15 , x + 4y = -2 x + 8y = 15 , x + 4y = -2 ?