Grade 8 Algebraic Proof Use algebra to construct

Grade 8 Algebraic Proof Use algebra to construct proofs. If you have any questions regarding these resources or come across any errors, please contact helpful-report@pixl. org. uk

Lesson Plan Lesson Overview Objective(s) Use algebra to construct proofs Prior Knowledge Algebraic notation and manipulation Duration 30 minutes Resources Print slides: 14 - 15 Grade 8 Equipment Progression of Learning What are the students learning? How are the students learning? (Activities & Differentiation) The concept of proof Using slide 4 and 5 introduce the concept of proof. 5 Standard grade 8 proofs Demonstration a standard GCSE algebraic proof that the sum of two consecutive square numbers is an odd number. Students to then attempt 4 further proofs using the concept understood from the example. 10 Algebraic proofs in exam questions (from specimen papers) Give students slide 15. This includes 4 exam questions related to objective. Students need to use notes from lesson to answer the questions. Ensure that all steps are shown. Relate to mark scheme to show the marks are allocated. 15 Next Steps Assessment PLC/Reformed Specification/Target 8/Algebra/Proof

Key Vocabulary Factorise Simplify Quadratic Linear Collect

What is proof? A proof is where you are asked to show that something is true using mathematics, in this case algebra. It could be simple: Prove that the area of a rectangle is 30 cm 2: 5 cm Or more complicated 6 cm Prove that the difference of two consecutive square numbers is an odd number. But you have to take the key information from a question and show what you are asked to.

Constructing a proof Looking at the simple example: Prove that the area of a rectangle is 30 cm 2: Area = length x width = 6 cm x 5 cm = 30 cm 2 as required 5 cm 6 cm Showing a fact and how the information you have fits that fact is a proof. The fact and the details must be stated.

Constructing a proof Looking at the complicated, grade 8 example: Prove that the sum of two consecutive square numbers is an odd number. A number = n The next number = (n+1) That number squared = n 2 That squared =(n+1)2 The sum of the squares is n 2+(n+1)2 You have now assembled the information you need to complete the proof.

So, the sum of the squares is n 2+(n+1)2 Expand brackets and simplify: =n 2+(n+1) Sentence to reason: =n 2+2 n+1 =2 n 2+2 n+1 2 n 2 is even 2 n is also even 1 is odd even + odd = odd Hence you have proven that the sum of consecutive squares is odd.

Practice Construct the algebraic proof for the following: 1) Prove that the sum of 3 consecutive even numbers is always a multiple of 6. 2) Show that (4 n+1)2 -(4 n-1)2 is always a multiple of 16 for positive integer values of n. 3) Prove that the difference between the squares of two consecutive integers is always equal to the sum of the two integers.

Answers 1) 2 n+(2 n+2)+(2 n+4) are 3 consecutive even numbers. 6 n+6 6 n is a multiple of 6, as is 6, therefore all combinations of three consecutive even numbers will be multiples of 6. 2) (4 n+1)2 = 16 n 2+8 n+1 (4 n-1)2 = 16 n 2 -8 n+1 If the second is subtracted from the first we are left with: 16 n. This is a multiple of 16 for integer values. 3) (n+1)2 - n 2 is the difference of 2 consecutive integers. n 2+2 n+1 -n 2 (2 n+1) is the sum of n and n+1, hence proven

Exam Question – Specimen Papers

Constructing a proof DEMO Prove that the sum of two consecutive square numbers is an odd number. Student Sheet 1 PRACTICE 1) Prove that the sum of 3 consecutive even numbers is always a multiple of 6. 2) Show that (4 n+1)2 -(4 n-1)2 is always a multiple of 16 for positive integer values of n. 3) Prove that the difference between the squares of two consecutive integers is always equal to the sum of the two integers.

Exam Question – Specimen Papers Student Sheet 3