3.4: Solving simultaneous equations using substitution method

1) Lesson Objectives:

You should be able to

• solve simultaneous equations by Substitution Method.

• to check you answer using a calculator.

Always look through all examples in textbook before lesson.

Solve the following simultaneous equations:

x + 3y  =  5

2x - 5y = -12

Steps:

1. Label both equations as (1) and (2)

2. Choose a variable that have coefficient 1.

3. Make sure the variable is the subject of the equation

4. Substitute the new equation into the other equation

5. Once you find one variable, remember to substitute and find the other variable

6. You must have 2 values, one for each variable as your answer

7. Check if you answer is correct by using your calculator

Using Calculator to check answer for simultaneous equations

NOTE: If you calculator is Casio fx-96SG Plus, please follow the steps.

STEPS:

1. Press MODE SETUP

2. Press 3 for EQN

3. Press 1: anX +bnY=Cn

4. You will see a square bracket with row a, b and c with column by the side 1 and 2.  There is 6 small rectangles in the bracket.

5. a and b represents your variables and c represents your constant. 

6. Make sure the equation is of the format   anX +bnY=Cn where

an represents coefficient of X,

bn represents coefficient of Y,

Cn represents your constant.

7. Key in the coefficient of each variable plus the constant with the correct sign.

8. When your finish keying in all 6 digits, press equal sign.

9. The first value will be the answer for variable x.  Press equal again and the next value will be the answer for variable y.