Systems - Substitution

What does it mean to substitute?

• to add different variables together and see what you get

• to graph and find the intersection

• guess and check

• to replace the value of a variable with an equivalent expression

Which one shows the correct substitution for the system?

y = 2x + 1

2x - 3y = 7

• 2(2x + 1) - 3y = 7

• 2x - 3(2x + 1) = 7

• y + 2x - 3y = 8

• 2x - 2x + 1 = 7

Simplify.

2x - 3(2x + 1) = 7

• 2x - 6x - 3 = 7

• 2x - 5x + 1 = 7

• 2x - 6x + 3 = 7

• 2x - 2x -3 = 7

Simplify.

2x - 6x - 3 = 7

• -7x = 7

• 4x + 3 = 7

• 8x - 3 = 7

• -4x - 3 = 7

Solve.

-4x - 3 = 7

• x = -2.5

• x = -40

• x = 0.4

• x = -1

If x = -2.5 what does y equal?

y = 2x + 1

2x - 3y = 7

• y = 0.75

• y = -4

• y = 5.5

• y = 9

Which one shows the correct substitution for the system?

x = 7 + y

y = 7 - 2x

• x = 7 + (7 - 2x)

• y = 7 - 7 + y

• x = 7 + 7

• 7 + y = 7 - 2x

Simplify.

x = 7 + (7 - 2x)

• x = 7 + 7 - 2x

• x = 49 - 14x

• x = 14 - 2x

• x = -2x

Solve.

x = 14 - 2x

• x = 2.1

• x = 12

• x = 14

• x = 4.6

If x = 4.6 what does y equal?

x = 7 + y

y = 7 - 2x

• y = -2.2

• y = 4.4

• y = 0.4

• y = -16.2