Question

Solve the following simultaneous equations:

$12x+15y+18=0$, $18x-7y+86=0$

• A. $x=-4;y=2$
• B. $x=1;y=0$
• C. $x=-3;y=5$
• D. $x=4;y=1$

Answer 1

The correct option is A $x=-4;y=2$

We pick either of the equations and write one variable in terms of the other.

Let us consider the equation $12x+15y+18=0$ and write it as

$x=\frac{-18-15y}{12}..........\left(1\right)$

Substitute the value of $x$ in Equation $18x-7y=-86$. We get

$18\left(\frac{-18-15y}{12}\right)-7y=-86\Rightarrow -54-45y-14y=-172\Rightarrow -59y=-118\Rightarrow y=2$

Therefore, $y=2$

Substituting this value of $y$ in Equation (1), we get

$x=\frac{-18-30}{12}=-\frac{48}{12}=-4$

Hence, the solution is $x=-4,y=2$.