The sum of the first three numbers in an arithmetic progression is 18. If the product of the first and the third term is 5 times the common difference. Find the three numbers..
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2, 6, 10
Step-by-step explanation:
Given The sum of the first three numbers in an arithmetic progression is 18. If the product of the first and the third term is 5 times the common difference. Find the three numbers.
Assume the three numbers as a + d, a, a - d.
Given sum of 3 terms in an A P is equal to 18
So a + d + a + a - d = 18
3 a = 18
a = 6
Now again product of first and third term is 5 times common difference(d)
so (a + d)(a - d) = 5 d
This is in the form of (a + b)(a - b) = a^2 - b^2
a ^2 - d^2 = 5 d
6^2 - d^2 = 5 d
d^2 + 5 d - 36 = 0
d^2 + 9 d - 4 d - 36 = 0
(d + 9)(d - 4) = 0
d = - 9, 4
Taking d = 4 we get 6 + 4 = 10, 6 - 4 = 2 and a = 6
So the numbers are 2, 6, 10
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