How do solve the following linear system?: $x+y=-4, 3x – 4y = 7$ ?

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Answer 1 · 2015-12-06T12:57:46

The solution for the system of equations is
$color(blue)(x=-9/7 , y=-19/7$

$color(blue)(3x)-4y = 7$ .........equation $(1)$

$x+y=-4$ , multiplying this equation by $3$
$color(blue)(3x) +3y = -12$ ....equation $(2)$

Solving by elimination

Subtracting equation $2$ from $1$ results in elimination of $color(blue)(3x$

$cancelcolor(blue)(3x)-4y = 7$
$-cancelcolor(blue)(3x) -3y = +12$

$-7y=19$

$y=19/(-7)$

$color(blue)(y=-19/(7)$

Finding $x$ by substituting $y$ in equation $2$ :
$x+y=-4$

$x=-4-y$

$x=-4-(-19/7)$

$x=-4+19/7$

$x=-28/7+19/7$

$color(blue)(x=-9/7$

How do solve the following linear system?: x+y=-4, 3x – 4y = 7 x+y=-4, 3x – 4y = 7 ?