18. The sum of three consecutive terms
in an A.P. is 6 and their product is -120.
Find the three numbers.
Answers
Answer:
Three consecutive number are -6, 2 ,10
Step-by-step explanation:
Let the three consecutive number be (a-d), a ,(a+d)
According to first given condition
a+d+a+a-d =6
3a=6
a=2 ..................(1)
put the values in the assumed consecutive number then it will be
(2-d), 2, ( 2+d)
According to second condition
(2-d)×2×(2+d)= -120
(4-d)(2-d)= -120
8+4d-4d-2d^2= -120
-2d^2= -120-8
d^2=-128/-2
d^2=64
d = 8..............(2)
from (1) and (2)
The three consecutive number are
a-d =2-8 =-6
a=2
a+d = 2+8 = 10
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GIVEN :
The sum of three terms of an AP = 6
The product of them = - 120.
TO FIND :
The terms.
SOLUTION:
Let the three terms be (a - d) , (a ), (a + d ).
Where a is the first term of an AP
d is the common difference of an AP.
=> a - d + a + a + d = 6
3a = 6
a = 6/3
a = 2
=> ( a - d) × ( a ) × ( a + d ) = - 120
a^3 - a (d^2) = - 120
(2) ^3 - 2( d^2) = - 120
8 + 120 = 2 (d^2)
128 = 2 (d^2)
64 = d^2
d = 8
The three terms are ,
=> 2 - 8 , 2 , 2 + 8
=> -6 , 2 , 10
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