if the sum of 7th and 11th term of an A.P is 60 and the product of 5th and 9th term is 12o .find the A.p?
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Answer:
-22, -15.5, -9......
Step-by-step explanation:
According to question,
a+6d+a+10d=60
2a+ 16d= 60............. equation (i)
a= 30-8d
(a+4d) (a+8d) = 120
a² + 12ad + 32d² = 120 ........ equation (ii)
Putting value of a in equation ii
(30-8d)² + 12(30-8d)d + 32d² = 120
900 + 64d² - 480d + 360d - 96d² + 32d² = 120
780 = 120d
d= 6.5
putting value of d in equation i
a= 30- 8(6.5)
a= -22
Therefore, A.P is -22, -15.5, -9......
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