Question

WILL GIVE BRAINLIEST AND 35 POINTS Solve this system of equations. $\left \{ {{3x+y=-21} \atop {y=4x}} \right.$

Answer 1

Answer:

$(-3,-12)$

$x=-3, y=-12$

Step-by-step explanation:

So we have the system:

$3x+y=-21\\y=4x$

To solve this, we can do some substitution. Substitute the y in the first equation for the 4x in the second:

$3x+y=-21\\3x+(4x)=-21$

Combine like terms:

$7x=-21$

Divide both sides by 7. The left side cancels:

$(7x)/7=(-21)/7\\x=-3$

So we determined that x is -3. Now, plug this number back into the second equation:

$y=4x\\y=4(-3)=-12$

So the solution is:

$(-3,-12)$

Answer 2

Answer:

$\Large \boxed{x=-3 \ } \\ \\ \Large \boxed{y=-12}$

Step-by-step explanation:

3x + y = -21

y = 4x

Substitue y = 4x in the first equation.

3x + 4x = -21

Combine like terms.

7x = -21

Divide both sides by 7.

x = -3

Let x = -3 for the second equation.

y = 4(-3)

Multiply.

y = -12

The solution for the system of equations is x = -3 and y = -12.