School unit : SMP N 2 Yogyakarta
Subject : Mathematics
Class/Semester : VIII/I
Time allocation : 15 minutes
Standard of competence : 1. Understanding algebraic form, function, and the equation of a straight line.
Basic competence : Determining the value of function
Indicators :
1. Determining the value of linear function
2. Determining the value of quadratic function
I. The purpose of learning :
1. Students are able to determine the value of linear function
2. Students are able to determine the value of quadratic function
II. Materials :
 |
f is a function then (x-1) states map of x and map of x is notated:
| |||
 | |||
For 
f (2)=2-1= 1
f (2)=2-1= 1f (2)=1 is called the function value of x =2
The value of function can be determined by the function formula. We can determine the value of function by substituting the value of x into the formula of function f(x).
Example :
1. A function f is defined by the formula f(x) = 2x – 1. Determine f(1)
Solution:
f(x) = 2x – 1
f(1) = 2(1) – 1
= 2 – 1
= 1
2. A function f is defined by the formula f(x) = 2x2 – 3x + 1. Determine the value of function f(x) for x = - 3
Solution :
f(x) = 2x2 – 3x + 1
f(-3) = 2(-3)2 – 3(-3) + 1
= 18 + 9 + 1
= 28
III. Learning Method :
Learning model : cooperative
Learning method : Expository, orally, interactive, drill
IV. Learning Scenario :
| Num. | Teacher’s Activities | Student’s Activities | Duration | ||||
| A. Pre-Teaching | 1 ½ minutes | ||||||
| 1. | Teacher are greeting all students, giving students a chance to pray, and checking the presences. Teacher : “Good afternoon students!” Teacher : “Before we start this class today, we must pray before. Let’s pray together!”. “Amin” Teacher : “ Who doesn’t join my class? Teacher : “Ready to study mathematics today, students? Please prepare your book and your stationery!” | Students answer the teacher’s greeting. Student : “Good afternoon, Miss” All student pray together. Student : “No one, Miss” Students prepare their books and their stationeries. | 1/2 minute | ||||
| 2. | Teacher gives apperception. Teacher reminds students about last topic, the definition of function. Teacher gives questions to all students in whole class. Teacher : “Yesterday, we learned about the definition of relation and function. What is the meaning of a function from set A to set B?” Teacher gives few minutes to student to remember, then teacher ask a student to answer that question. Teacher : “Sulis, what is the meaning of a function from set A to set B? ” Teacher : “Yeah, That’s right. Thank you Sulis” | Student answers teacher’s question about the definition of function. Sulis : “Function from set A to set B is a special relation that pairs every element in A to exact one element in B” |  minute | ||||
| 3. | Teacher tells about the topic that we will learn today and the purpose which we will reach in this learning. Teacher: “Today, we will learn how to determine the value of function. From this learning today, we are able to determine the value of linear function and quadratic function.” | Students listen teacher’s explanation. | 1/4 minute | ||||
| B. Main Activity | 12 minutes | ||||||
| 1. | Teacher draws two sets, set K and set L on the white board. | Students consider teacher’s explanation. | ¾ minute | ||||
| 2. | Teacher asks the relation between set K and set L to all students in whole class. Teacher : “What is the relation that connect set K and set L? Teacher asks a student. “What is the relation, Yustia?” Teacher menanyakan ke student lain. “How about you, Ayu?” Teacher asks the reason to a same student. “What is the reason Ayu, so you can state that relation is x-1? Teacher: “Good, Ayu” | Students consider teacher’s explanation. Yustia says “ x-1, Miss” Ayu : “Same, Miss” Ayu : “Because 2-1=1, 3-2=1, 4-3=1,and so on. Thus, the relation is x-1, Miss” | ½ minute | ||||
| 3. | Teacher explains again the relation between set K and set L on the whiteboard. Teacher : “Generally, if we take x,  then the codomain in L is (x-1). In arrow diagram, it is written 𝑓:𝑥→(𝑥−1) (pronounce: f is mapping x to x-1) | |  minute | ||||
| 4. | Teacher explains two sets, K and L on the white board. Teacher asks to students “ Is f a function?” Teacher: “Why do you conclude that f is a function? What is the reason?” Teacher asks to a student, “What is the reason, Septi?” Teacher : “That’s right. Thank you Septi” | Student: “Yes. It is…” Septi : “Since every element in K has exactly one pair in L” |  minute. | ||||
| 5. | Teacher writes on the blackboard then she explains to students.
Teacher: “f(x)= x-1 is an example of linear function formula. Why is it called linear?” Teacher: “What is the reason, Auri?” Teacher: “Good, Auri. Thank you” Teacher aks to all students in whole class, “ Is f(x) = 2x2 – 3x + 1 a linear function formula too?” Teacher: “So, what is the type of this function?” Teacher: “What is the type of this function, Maratu?” Teacher: “Why do you stated it, Maratu?” | Students consider teacher’s explanation. Auri : “Because the highest exponent is 1” Students : “No, It isn’t” Maratu : “ It is quadratic function formula” Maratu: “ Because the highest exponent is 2. | 1  minutes. | ||||
| 6. | Teacher writes on the whiteboard and explains to all students. Teacher says: “Consider the function f For x=2  f (2)=2-1= 1f (2)=1 is called the function value of x = 2” | Students consider teacher’s explanation. |  minute | ||||
| 7. | Teacher gives two examples. Teacher calls two students to solve example 1 and example 2. Teacher : “ Tri and Etik, please help me to solve example 1 and example 2 in front of class.” Teacher : “Okay, please Tri and Etik explain to your friends how to solve that? Tri first, and then Etik” Teacher : “Is Tri’s work true, Tyo?” Teacher: “How about Etik’s work, Purwoko?” Teacher : “Thank you Tri, Etik.” “Give applause to your friend, Tri and Etik” | Students consider teacher’s explanation. Tyo: “Yes, it is.” Purwoko: “Yes. it is” Students give applause. | 2  minutes | ||||
| 8. | Teacher asks to all students “Any question about how to determine the value of function?” . | Students: “Not yet, Miss” |  minutes | ||||
| 9. | Teacher gives students exercise to be solved. Teacher: “Write the answer in your book. If you find problems, ask your friend.” Teacher monitors each student, guide a student whom has a problem related how to determine the value of function. | Students solve the exercises. | 5 minutes | ||||
| C. Closing | 1  minutes | ||||||
| 1. | Teacher asks a student to reflect the topic today. Teacher : “Today, what is we learned? Please tell us, Bowo” Teacher: “How to determine the value of function? Please, explain us, Oky!” Teacher: “Good Bowo, Oky. To determine the value of function, we just only substituting x to function formula.” | Bowo : “Today we learn about how to determine the value of function?” Oky: “By substituting x to function formula” |  minute | ||||
| 2. | Teacher gives home works to all students, solve the next exercises. Teacher : “That exercise is your homework. Write on your book, and next week it will be collected.” | Students note the homework. |  minute | ||||
| 3. | Teacher tells the topic for next meeting. Teacher: “Next week, we will learn about function again, how to determine function formula, if the value of function was known.” | Students listen teacher’s explanation. | minute | ||||
| 4. | Teacher closes the meeting with praying and greeting. Teacher : “before, we close this class, we pray together. Let’s pray together. Amin” “Good afternoon, students!” | Students: “Good afternoon, Miss” |  minute | ||||
V. Media/Reference :
Media : exercise about the value of function
Reference :
Marsigit. 2010. Mathematics For Junior High School 2Year VIII. Jakarta: Yudhistira.
Dewi Nuharini & Tri Wahyuni. 2008. Matematika Konsep dan
Aplikasinya 2. Jakarta : Pusat Perbukuan Departemen Pendidikan
Nasional.
VI. Assessment
1. The technical of assessment : written assessment
2. The form of assessment : essay
3. Instrument :
A. Exercise
1. A function f is defined by the formula 
. Determine the value of function for x = -3, -1, 0, and 2
. Determine the value of function for x = -3, -1, 0, and 22. A function f is defined by the formula f(x) = x2 – 5x. Determine the value of function f(x) for :
(i) x = -2
(ii) x = -1
(iii) x = 2
(iv) x = 3
3. A function f is defined by the formula f(x) = 2x2 – x+3. Determine the value of f(4) and f(6)
4. A function f is defined by 
Determine the value of function f(x) for x = -2,-1,0, 1, and 2 .
Determine the value of function f(x) for x = -2,-1,0, 1, and 2 .5. A function f is defined by the formula f(x) = 7x-4. Determine the value of f(2) and f(3).
B. Answer key
1. f(-3) = 4(-3)-1 = -13
f(-1) = 4(-1)-1 = -5
f(0) = 4(0)-1 = -1
f(2) = 4(2)-1 = 7
2. (i) f(-2) = (-2)2-5(-2) = 14
(ii) f(-1) = (-1)2-5(-1) =6
(iii) f(2) = (2)2-5(2) = -6
(iv) f(3) = (3)2-5(3) = -6
3. f(4) = 2(4)2-4+3 = 31
f(6) = 2(6)2-6+3 = 69
4. f(-2) =(-2)2-5(-2)+7 = 21
f(-1) =(-1)2-5(-1)+7 = 13
f(0) =(0)2-5(0)+7 = 7
f(1) =(1)2-5(1)+7 = 3
f(2) =(2)2-5(2)+7 = 1
5. f(2) = 7(2)-4 = 10
f(3) = 7(3)-4 = 17
| Yogyakarta, April 3th 2012 | |
| Lecturer, Dr. Marsigit | University student, Dewi Widowati |
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