If the equation
has three roots and they are in an arithmetic progression.
Find the value of k.
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Let the three real roots be a , b and c .
From the topic of the "sum and product of roots",
we get :
a + b + c = 3 3 ---------------------------(*)
a b + b c + c a = 3 5 4 --------------------(**)
a b c = k ---------------------------------------( * )
From equation (*):
Since a , b and c are in an arithmetic progression, let the common difference be n .
So, ( b − n ) + b + ( b + n ) = 3 3
3 b = 3 3
b = 1 1
Subsituting the value of b into (**), we get:
1 1 ( a + c ) + a c = 3 5 4
1 1 [ ( b − n ) + ( b + n ) ] + a c = 3 5 4
2 2 b + a c = 3 5 4
2 4 2 + a c = 3 5 4
a c = 1 1 2
From ( * ):
a b c = k
( 1 1 2 ) ( 1 1 ) = k
k = 1 2 3 2