1. Teaching Point: I can evaluate an expression or check my work by substituting in a variable and applying my knowledge of PEMDAS. Do-now: 1)4(3) +7 – 1 2)3-7 2 (2) 3)12/6(2)

2. NOTES: Using Substitution Substitution means to put a number into the place of a variable and perform the given operations. (Using the order of operations) For example: 5x+6, x = 10 5(10) +6 50+6 56 You can substitute any number you want. Take the same problem and change the value of x. 5x +6, x = 2 5(3) + 6 15 +6 21

3. Nota Bene!! A number next to a variable (the coefficient) means multiply. So 6f means 6 times f. So if you are given evaluate 6f, f =2, the answer IS NOT 62!! It is 12!! 6(2) = 12

4. Together: 1) n/4 -3, n=24 2) 9+(3d 2 ), d=2

5. On your own: 1)4w-5, w = 12 2) 1/2j +6, j=10 3) (y 3 -12)/ 3, y=3

6. THINK!!!! Hmmmm…… A student evaluated the following expression and got the answer to be 53. What did they do wrong? 5k +3, k=2 55

7. Why do we learn to substitute? The reason we substitute is to check our work. If you know the answer then you can go back and put it in to see if it makes sense. BUT you need to know a few things about EQUATIONS. Equations must be equal. That’s the whole point. Both sides have to equal each other. If they don’t something is WRONG!!

8. Take the equation 2x = 6. You and your friend solve it, and you get different answers. You get 3, and he gets 4. Who is right? How do you know? Can you prove it?

9. By using substitution, you can prove that you are right and the answer is 3. 2x = 6 2(3) = 6 TRUE 2x = 6 2(4) = 6 FALSE! 2(4) =8!