# Two Aps Have The Same Common Difference. The First Term Of One Of These Is –1 And That Of The Other Is – 8. The Difference Between Their 4Th Terms Is

tl;dr
The difference between the 4th terms of the two arithmetic progressions with a first term of -1 and -8 respectively is 7.

The concept of arithmetic progression (AP) is a fundamental concept in mathematics. An arithmetic progression is a sequence of numbers where the difference between any two consecutive terms is constant. In this article, we will explore the scenario where two arithmetic progressions have the same common difference, but their initial terms are different. Specifically, we will discuss the case where the first term of one progression is -1, and the first term of the other progression is -8.

Before delving into the comparison, let's make sure we have a clear understanding of arithmetic progression. In an arithmetic progression, each term is found by adding a constant difference to the previous term. For example, if the first term is 'a' and the common difference is 'd', then the second term will be 'a + d', the third term will be 'a + 2d', and so on. Mathematically, an arithmetic progression can be written as:

a, a + d, a + 2d, a + 3d, ...

Now, let's consider the two arithmetic progressions in question. The first progression has a first term of -1, so we can write it as:

-1, -1 + d, -1 + 2d, -1 + 3d, ...

The second progression has a first term of -8, so we can write it as:

-8, -8 + d, -8 + 2d, -8 + 3d, ...

We are interested in the difference between their 4th terms. To find that, we need to determine the 4th term for each progression and calculate the difference between them.

Let's calculate the 4th term for the first progression. Using the AP formula, we can plug in the values:

4th term = -1 + 3d

For the second progression, we can do the same:

4th term = -8 + 3d

Now, to find the difference between their 4th terms, we subtract the two expressions:

Difference = (-1 + 3d) - (-8 + 3d)

= -1 + 3d + 8 - 3d

= 7

Therefore, the difference between the 4th terms of the two arithmetic progressions is 7.

This result is quite interesting because it shows that even though the initial terms of the progressions are different, they still have the same common difference. In other words, both progressions increase by the same amount at each step. This fact can be observed by examining the equations for the two progressions. In both cases, the terms are formed by adding the common difference 'd' to the previous term. This implies that both progressions have the same pattern of growth, despite starting from different points.

To further illustrate this point, let's take a closer look at the progression with a first term of -1:

-1, -1 + d, -1 + 2d, -1 + 3d, ...

Now, let's rewrite the terms by replacing 'd' with the common difference '7':

-1, -1 + 7, -1 + 2(7), -1 + 3(7), ...

Simplifying, we get:

-1, 6, 13, 20, ...

Now, let's examine the progression with a first term of -8:

-8, -8 + d, -8 + 2d, -8 + 3d, ...

Again, replace 'd' with '7':

-8, -8 + 7, -8 + 2(7), -8 + 3(7), ...

Simplifying, we get:

-8, -1, 6, 13, ...

As we can see, both progressions have the same terms starting from the second term onwards. This confirms that the two progressions have the same common difference.

Understanding and recognizing these patterns in arithmetic progressions is crucial in various fields, including mathematics, physics, and computer science. For example, in physics, the concept of motion follows an arithmetic progression in some cases. Understanding the patterns and relationships between terms can help in solving problems related to displacement, velocity, and acceleration. In computer science, the concept of iteration relies heavily on arithmetic progressions to perform repetitive tasks efficiently.

In conclusion, in this article, we explored the scenario where two arithmetic progressions have the same common difference, but their initial terms are different. In particular, we examined the case where the first term of one progression is -1, and the first term of the other progression is -8. Although the initial terms are distinct, we discovered that both progressions have the same common difference. This fact demonstrates that both progressions increase by the same amount at each step, despite starting from different points. Understanding these patterns and relationships can greatly enhance our understanding of mathematics and its applications in various fields.