Problem 10 - Algebra and Trigonometry

Question

Write the first six terms of each arithmetic sequence. $$ a_{n}=a_{n-1}+4, a_{1}=-7 $$

Step-by-Step Solution

Answer

The first six terms of the arithmetic sequence are -7, -3, 1, 5, 9, 13.

Step 1: Identify Initial Term

From the problem, we understand that the initial term is given and it is \(a_{1}=-7\). So, this is our first term.

Step 2: Calculate Second Term

The formula for the sequence is \(a_{n} = a_{n-1} + 4\). By substituting n=2 in the formula, we get: \(a_{2} = a_{1} + 4\). Using the value of \(a_{1}\) as -7, calculate the second term, \(a_{2} = -7 + 4 = -3\). So, the second term is -3.

Step 3: Calculate Third Term

Same as above, substitute n=3 in the formula, \(a_{3} = a_{2} + 4\). Using the value of \(a_{2}\) as -3, calculate the third term. Therefore, \(a_{3} = -3 + 4 = 1\). So, the third term is 1.

Step 4: Calculate Fourth, Fifth and Sixth Terms

By following the exact same steps as before, calculate the remaining terms. Therefore, \(a_{4} = a_{3} + 4 = 1 + 4 = 5\), \(a_{5} = a_{4} + 4 = 5 + 4 = 9\), and \(a_{6} = a_{5} + 4 = 9 + 4 = 13\). So, the fourth, fifth and sixth terms are 5, 9 and 13 respectively.

Key Concepts

Arithmetic Sequence Terms

Arithmetic sequences are fundamental constructs in mathematics where each term is derived by adding a constant to the previous term. This constant is known as the common difference. For instance, with the sequence given by the rule ( a_{n}=a_{n-1}+4, a_{1}=-7 ), notice that the common difference here is 4. Each term is simply 4 more than the term before it.

The initial term of the sequence, often denoted as ( a_{1} ), is crucial because it serves as the starting point. In this example, the initial term is ( a_{1}=-7 ). Understanding the role of the initial term and the common difference allow us to predict any term in the sequence without having to write out all the preceding terms, which is particularly handy for long sequences.

Sequence Term Calculation

Calculating terms in an arithmetic sequence involves a simple yet powerful formula: ( a_{n}=a_{1}+(n-1)d ), where ( a_{n} ) is the term you're finding, ( a_{1} ) is the first term, ( n ) is the term position, and ( d ) is the common difference. This direct approach is efficient and reduces errors that might come from manually adding the common difference multiple times.

For example, to find the 5th term of our sequence without relying on the preceding ones, we'd plug the appropriate values into the formula: ( a_{5}=a_{1}+(5-1)(4) ), resulting in ( a_{5}=-7+16 ) or ( a_{5}=9 ). This gives us a quick calculation for any term's value.

Arithmetic Progression

An arithmetic progression is another term for an arithmetic sequence. It's a series of numbers in which the difference of any two successive members is a constant. This form of progression showcases a smooth and uniform growth or decrease in values, which is predictable and easily understandable.

Illustrating the progression aspect of the sequence, if we list the first six terms - determined using the steps provided or a general formula - we see a clear upward progression: -7, -3, 1, 5, 9, and 13. Each new term is progressing by overtly adding the number 4. Arithmetic progressions are everywhere in real life, from the design of stair steps to the arrangement of seats in a theater, and they are especially appreciated for their simplicity and clarity in conveying increments or decrements.