Question

Which ordered pair is the solution to the system of equations?
-3x+4y=-20
x+4y=-4
A.
(8, 1)

B.
(−12, 2)

C.
(−4, −8)

D.
(4, −2)

Answer 1

This is what I got:

x+4y=−4;−3x+4y=−20
Step: Solvex+4y=−4for x:
x+4y+−4y=−4+−4y(Add -4y to both sides)
x=−4y−4
Step: Substitute−4y−4forxin−3x+4y=−20:
−3x+4y=−20
−3(−4y−4)+4y=−20
16y+12=−20(Simplify both sides of the equation)
16y+12+−12=−20+−12(Add -12 to both sides)
16y=−32
16y16=−3216(Divide both sides by 16)
y=−2
Step: Substitute−2foryinx=−4y−4:
x=−4y−4
x=(−4)(−2)−4
x=4(Simplify both sides of the equation)
Answer:
x=4 and y=−2