Question

Solve the equation using substitution method:
$3x+y+1=0$ and $3x-4y=10$

• A. (0.4, 2.2)
• B. (0.4, -2.2)
• C. (0.4, 1.2)
• D. (-0.4, 2.2)

Answer 1

The correct option is B (0.4, -2.2)

$3x+y+1=0$ ------- (1)
$3x-4y=10$ --------(2)
From equation (1)
$3x+y=-1$
$y=-1-3x$
Substitute the value of $y$ in equation (2)
$3x-4(-1-3x)=10$
$3x+4+12x=10$
$15x=10-4$
$x=\frac{6}{15}$ or $\frac{2}{5}\simeq 0.4$
The substitute the value of x in equation (1)
$3x+y=-1$
$3\left(\frac{2}{5}\right)+y=-1$
$6+5y=-5$
$5y=-5-6$
$5y=-11$
$y=\frac{-11}{5}$ or -2.2
therefore solution is $x=0.4$ and $y=-2.2$