Question

Find the 70th term of the arithmetic sequence

Answer 1

753

Explanation:

Arithmetic sequences are sequences that change by a constant factor.

Explicit Rule

The formula that describes an arithmetic sequence is called the "explicit rule". This formula is f(x) = f(1) + d(x-1). Sometimes the rule will be written with
`a_(n)` instead of f(x) but the equations are still the same.

In this equation, f(1) is the first term of the sequence, d is the common difference, and x is the term. The common difference is the factor that the sequence changes by.

Setting Up the Equation

To set up the equation, we need to find f(1) and d.

The first term, f(1), is directly given to us in the equation. The first term written is -6, so f(1)=-6.

It is slightly more difficult to find d. But, one easy way to find d is by subtracting terms. Take the second term, 5, and subtract the first term, -6.

• 5 - (-6) = 11

So, d = 11. Each term in the sequence increases by 11.

The final equation is f(x) = -6 + 11(x-1).

Finding the 70th Term

Now, all we have to do is plug 70 in for x. To find any term in the sequence, all you have to do is plug the term number in for x.

• f(70) = -6 + 11(70-1)
• f(70) = 753

The 70th term in the sequence is 753.