Three numbers form a H.P. The sum of the numbers is 11 and the sum
of the reciprocals is one. Find the numbers.
Answers
a+b+c = 11 --------------(1)
1/a + 1/b + 1/c = 1 --------(2)
a,b,c are in H.P. then 1/a,1/b,1/c are in A.P.
1/a + 1/c = 2/b
put in equation (2)
1/b + 2/b = 1
3/b = 1
b = 3
a+c = 8 ----------------(3)
1/a + 1/c = 2/3
(a+c)/ac = 2/3
ac = 12
(a-c)² = (a+c)² - 4ac
= 64 - 48
= 16
a-c = 4 ---------------(4)
(3) + (4)
2a = 12
a = 6
c = 2
Given : Three numbers form a H.P. the sum of the numbers is 11 and the sum of their reciprocals is 1
To Find : Find the numbers.
Solution:
Let say three numbers are
1/a , 1/b . 1/c
Three numbers form a H.P.
=> a , b & c are in ap
=> 2b = a + c
1/a + 1/b + 1/c = 11
sum of their reciprocals is 1
=> a + b + c = 1
=> 2b + b = 1
=> 3b = 1
=> 3 = 1/b
1/a + 3 + 1/c = 11
=> 1/a + 1/c = 8
=> c + a = 8ac
=> 2b = 8ac
=> 2/3 = 8ac
=> 1/12 = ac
a + c = 2/3
=> x² - (2/3)x + 1/12 = 0
=> 12x² - 8x + 1 = 0
=> 12x² - 6x - 2x + 1 = 0
=> 6x(2x - 1) - 1(2x - 1) = 0
=> x = 1/6 , 1/2
a & c are 1/6 & 1/2
1/a , 1/c are 6 & 2
Hence numbers are
2 , 3 , 6
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