If is a cubic polynomial satisfying the above equations, find the value of
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Let f ( x ) = a x 3 + b x 2 + c x + d
From the four pieces of information we form the equations:
a + b + c + d = 1
− a + b − c + d = 1 1
− 8 a + 4 b − 2 c + d = 2 2
8 a + 4 b + 2 c + d = 1 4
Adding the first to the second and simplifying, we have b + d = 6 . Doing the same for the other two equations we have 4 b + d = 1 8 . Note that the question is looking for f ( 0 ) which is simply the value of d so we need only solve for d .
( 4 b + d ) − ( b + d ) = 1 8 − 6
3 b = 1 2
b = 4
4 + d = 6
d = 6 − 4 = 2 .