Question

16 POINTS

More than one answer



What is the solution of the system?

Use either the substitution method or the elimination method.

7x + 2y = −19

−x + 2y = 21



(8, 5)
There are an infinite number of solutions.
(−5, −8)
(−5, 8)

Answer 1

Solve the following system using elimination:
{7 x + 2 y = -19 | (equation 1)
{2 y - x = 21 | (equation 2)

Add 1/7 × (equation 1) to equation 2:
{7 x + 2 y = -19 | (equation 1)
{0 x+(16 y)/7 = 128/7 | (equation 2)

Multiply equation 2 by 7/16:
{7 x + 2 y = -19 | (equation 1)
{0 x+y = 8 | (equation 2)

Subtract 2 × (equation 2) from equation 1:
{7 x+0 y = -35 | (equation 1)
{0 x+y = 8 | (equation 2)

Divide equation 1 by 7:
{x+0 y = -5 | (equation 1)
{0 x+y = 8 | (equation 2)

Collect results:
Answer: {x = -5, y = 8