5.2b Basic Substitution for system of equations

5.2b Basic Substitution for system of equations

Substitution means to replace a variable with something that is equal to it.

• 3x + 2y = 2

• y = 4

• Replace the "y" in the first equation with 4

• 3x + 2(4) =2

• Now solve for x: 3x + 8 = 2

• 3x = -6

• x = -2

Multiple Choice

Solve for 'x' if y = -2

4x - 5y = 22

• x = 8

• x = -8

• x = -3

• x = 3

Multiple Choice

Find "y" if x = -4 in the equation below.

2x - 6y = 4

• y = -2

• y = 2

• y = 4

• y = -4

Multiple Choice

Solve for "x" and "y" if y = 2x in the equation below:

-4x + 5y = -12

• (2, 4)

• (-2, 4)

• (2, -4)

• (-2, -4)

Solving a system by basic substitution is done the same way.

• Given two equations:

• 3x - 4y = 6

• and y = -3

• Subititute the value of y into the first equation

• 3x - 4(-3) = 6 and solve for x

• Express the answer in an ordered pair: (-2, -3)

Multiple Choice

Solve the following system of equations by substitution:

3x - y = -7

y = -2

• (3, -2)

• (-3. -2)

• (-2, 3)

• -2, -3)

Multiple Choice

Solve the following system by substitution:

-5x - 4y = 6

x = 2

• (2, -4)

• (2, 4)

• (-4, 2)

• 4, 2)

Multiple Choice

Solve the following system by substitution:

-7x - 3y = 4

y = -2x

• (4, 8)

• (4, -8)

• (-4, 8)

• (-4, -8)

Multiple Choice

Solve the following system by substitution:

-4x + 9y = -6

x = 3y

• (6, 2)

• (6, -2)

• (-6, 2)

• (-6, -2)