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Sagot :
Answer:
The terms are - 1, 7 and 15.
Step-by-step explanation:
Let the terms be a-d, a, a+d.
ATQ, a-d+a+a+d=21, a=7 and a+d-(a-d+a)=9. 2d-a=9, d=8. The terms are - 1, 7 and 15.
The first three terms will be : -1, 7, 15
We have sum of first three terms of an arithmetic series is 21. It is given that if the sum of the first two terms is subtracted from the third term then it would be 9.
We have to find the three terms of the series.
What is Arithmetic progression or sequence?
An arithmetic progression or sequence with common difference [tex]d[/tex] is given as -
a, a + d, a + 2d, a + 3d .....
According to the question -
a + (a + d) + (a + 2d) = 21
3a + 3d = 21
3(a + d)=21
a + d = 7 (Eqn. 1)
(a + 2d) - (a + a + d) = 9
a + 2d - a - a - d = 9
d - a = 9
a = d - 9
Substituting the value of 'a' in Eqn. 1, we get -
d - 9 + d = 7
2d - 9 = 7
2d = 16
d = 8
Therefore -
a = 8 - 9
a = -1
The three terms are -
a = -1
a + d = -1 + 8 = 7
a + 2d = -1 + 2 x 8 = 15
Hence, the first three terms will be - -1, 7, 15
To solve more questions on Arithmetic Sequences and finding the terms, visit the link below -
https://brainly.com/question/20384906
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