Mathematics Grade 9 15 min

Evaluate variable expressions for number sequences

Evaluate variable expressions for number sequences

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1

Introduction & Learning Objectives

Learning Objectives Define a number sequence and the variable expression that generates it. Substitute a given term number (n) into a variable expression to find the value of that term. Evaluate linear expressions (e.g., an + b) for given values of n. Evaluate quadratic expressions (e.g., an^2 + bn + c) for given values of n. Evaluate expressions involving radicals or exponents for given values of n. Generate the first 'k' terms of a sequence given its variable expression. Ever wonder how video games create progressively harder levels or how your savings account grows over time? 📈 It's all about predictable patterns called sequences! This tutorial will teach you how to use a formula, called a variable expression, to find any specific number in a pattern or s...
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Key Concepts & Vocabulary

TermDefinitionExample Number SequenceAn ordered list of numbers, where each number follows a specific rule or pattern.The list 5, 8, 11, 14, ... is a number sequence where each number is 3 more than the previous one. TermEach individual number in a sequence. We often use a subscript to denote the term, like T_n.In the sequence 5, 8, 11, 14, ..., the third term (T_3) is 11. Term Number (n)The position of a term in a sequence. It's almost always a positive integer starting from n=1.For the term 11 in the sequence 5, 8, 11, 14, ..., the term number is n=3. Variable Expression (Rule)An algebraic formula that describes the relationship between a term's value and its position (n) in the sequence.The expression 3n + 2 generates the sequence 5, 8, 11, 14, ... EvaluateTo substitute a spe...
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Core Formulas

Substitution Principle To evaluate an expression for a variable, replace every instance of the variable with its given numerical value. This is the fundamental action for this topic. If you are asked to find the 10th term (n=10) of a sequence with the rule T_n = 5n - 1, you replace 'n' with '10' to get T_10 = 5(10) - 1. General Form of a Linear Expression T_n = an + b This rule generates arithmetic sequences where there is a constant difference between terms. To find the value of any term (T_n), you substitute its position (n) into the formula. General Form of a Quadratic Expression T_n = an^2 + bn + c This rule generates sequences where the second difference is constant. To evaluate, you must follow the order of operations, calculating the expone...

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Sample Practice Questions

Easy
In the context of number sequences, what does the variable 'n' typically represent?
A.The value of the term
B.The difference between terms
C.The position of the term in the sequence
D.The total number of terms in the sequence
Easy
A sequence is generated by the variable expression T_n = 4n + 5. What is the value of the 3rd term?
A.9
B.12
C.17
D.23
Easy
What is the 8th term of the sequence defined by the rule a_n = n^2 + 1?
A.17
B.65
C.81
D.64

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