Question

Solve the system of equations using elimination 3c - 8d =7 and c + 2d = -7

Answer 1

Given.

`(3c-8d=7)=(c+2d=-7)`

Multiply 4 to the second equation.

`4(c+2d=-7)`

`3c+8d=-28`

Compare the like terms.

`4c+3c-8d+8d=7-28`

Solve.

`7c=-21`

Divide 7 to both sides

`(7c)/(7)=(-21)/(7)`

`c=-3`

Substitute (-3) for c into the original second equation.

`c+2d=-7`

`-3+2d=-7`

Add (3) to both sides.

`(-3+2d=-7)+3`

`2d=-4`

Divide (2) to both sides.

`(2d)/(2)=(-4)/(2)`

`d=-2`

Check your work.

`3(-3)-8(-2)=7`

`-9+16=7`

`7=7`

`c+2d=-7`

`-3+2(-2)=-7`

`-3-4=-7`

`-7=-7`

Therefore your answer is.

`c=-3\\d=-2`

Answer 2

d=-2 c=-3

Explanation:

3c-8d=7

4(c+2d=-7)

3c-8d=7

4c+8d=-28

4c+3c-8d+8d=7-28

7c=-21

c=-3

c+2d=-7

-3+2d=-7

2d=-4

d=-2