There are five terms in an arithmetic progression. The sum of these terms is 55, and the fourth term is five more than the sum of the first two terms. Find the terms of the arithmetic progression.



Answer :

To find the terms of the arithmetic progression (AP) given the sum of the terms and the relationship between the terms, we will follow these steps:

1. Identify the form of the terms in the AP:
- Let the first term be [tex]\( a \)[/tex] and the common difference be [tex]\( d \)[/tex].
- The five terms of the AP can be expressed as: [tex]\( a \)[/tex], [tex]\( a + d \)[/tex], [tex]\( a + 2d \)[/tex], [tex]\( a + 3d \)[/tex], [tex]\( a + 4d \)[/tex].

2. Set up the sum equation for the AP:
- The sum of these five terms is given as 55.
- Using the sum formula for an arithmetic progression:
[tex]\[ \text{Sum} = \frac{n}{2} \times (\text{First term} + \text{Last term}) \][/tex]
- With [tex]\( n = 5 \)[/tex], the first term [tex]\( a \)[/tex], and the last term [tex]\( a + 4d \)[/tex]:
[tex]\[ \text{Sum} = \frac{5}{2} \times (a + (a + 4d)) = 55 \][/tex]
- Simplifying this equation:
[tex]\[ \frac{5}{2} \times (2a + 4d) = 55 \][/tex]
[tex]\[ 5(a + 2d) = 55 \][/tex]
[tex]\[ a + 2d = 11 \quad \text{(1)} \][/tex]

3. Set up the condition involving the fourth term:
- We are given that the fourth term ([tex]\( a + 3d \)[/tex]) is five more than the sum of the first two terms ([tex]\( a + (a + d) \)[/tex]):
[tex]\[ a + 3d = (a + (a + d)) + 5 \][/tex]
- Simplifying this equation:
[tex]\[ a + 3d = 2a + d + 5 \][/tex]
[tex]\[ a + 3d - 2a - d = 5 \][/tex]
[tex]\[ -a + 2d = 5 \][/tex]
[tex]\[ a - 2d = -5 \quad \text{(2)} \][/tex]

4. Solve the simultaneous equations:
- From equations (1) and (2):
[tex]\[ a + 2d = 11 \][/tex]
[tex]\[ a - 2d = -5 \][/tex]
- Adding these two equations:
[tex]\[ (a + 2d) + (a - 2d) = 11 + (-5) \][/tex]
[tex]\[ 2a = 6 \][/tex]
[tex]\[ a = 3 \][/tex]
- Substitute [tex]\( a = 3 \)[/tex] back into equation (1):
[tex]\[ 3 + 2d = 11 \][/tex]
[tex]\[ 2d = 8 \][/tex]
[tex]\[ d = 4 \][/tex]

5. Determine the terms of the AP:
- Using [tex]\( a = 3 \)[/tex] and [tex]\( d = 4 \)[/tex]:
- First term: [tex]\( a = 3 \)[/tex]
- Second term: [tex]\( a + d = 3 + 4 = 7 \)[/tex]
- Third term: [tex]\( a + 2d = 3 + 8 = 11 \)[/tex]
- Fourth term: [tex]\( a + 3d = 3 + 12 = 15 \)[/tex]
- Fifth term: [tex]\( a + 4d = 3 + 16 = 19 \)[/tex]

Thus, the terms of the arithmetic progression are:
[tex]\[ \boxed{3, 7, 11, 15, 19} \][/tex]