F ( x ) is a monic cubic polynomial where
F ( 0 ) = 1 , F ( 1 7 ) = 5 4 9 2 , F ( 2 3 ) = 1 3 2 2 6 .
Find the sum of its coefficients.
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
good solution for an easy problem
Let F ( x ) = x 3 + a x 2 + b x + c . Then, we have:
⎩ ⎪ ⎨ ⎪ ⎧ F ( 0 ) = 0 + 0 + 0 + c = 1 F ( 1 7 ) = 4 9 1 3 + 2 8 9 a + 1 7 b + 1 = 5 4 9 2 F ( 2 3 ) = 1 2 1 6 7 + 5 2 9 a + 2 3 b + 1 = 1 3 2 2 6 ⇒ c = 1 ⇒ 2 8 9 a + 1 7 b = 5 7 8 ⇒ 5 2 9 a + 2 3 b = 1 0 5 8 . . . ( 1 ) . . . ( 2 )
{ E q . 1 × 2 3 : E q . 2 × 1 7 : 6 6 4 7 a + 3 9 1 b = 1 3 2 9 4 8 9 9 3 a + 3 9 1 b = 1 7 9 8 6 . . . ( 1 a ) . . . ( 2 a )
E q . 2 a − E q . 1 a : 2 3 4 6 a + 0 = 4 6 9 2 ⇒ a = 2
Substituting a = 2 in E q . 1 : 5 7 8 + 1 7 b = 5 7 8 ⇒ b = 0
Therefore the sum of coefficients = 1 + a + b + c = 1 + 2 + 0 + 1 = 4
nice solution
Problem Loading...
Note Loading...
Set Loading...
L e t t h e p o l y n o m i a l b e F ( x ) = x 3 + a x 2 + b x + c F ( 0 ) = 1 ⟹ c = 1 . . . . . . ( 1 ) F ( 1 7 ) = 5 4 9 2 ⟹ 1 7 3 + 1 7 2 a + 1 7 b = 5 4 9 1 = 1 7 ∗ 3 2 3 ∴ 1 7 2 + 1 7 a + b = 3 2 3 ⟹ 1 7 a + b = 3 4 . . . . . . ( 2 ) F ( 2 3 ) = 1 3 2 2 6 ⟹ 2 3 3 + 2 3 2 a + 2 3 b = 1 3 2 2 5 = 2 3 ∗ 5 7 5 ∴ 2 3 2 + 2 3 a + b = 5 7 5 ⟹ 2 3 a + b = 4 6 . . . . . . ( 3 ) S o l v i n g ( 2 ) a n d ( 3 ) w e g e t a = 2 a n d b = 0 . . . . . ( 4 ) L e a d i n g c o e f f i c i e n t i s 1 a n d f r o m ( 1 ) a n d ( 4 ) A n s w e r = 1 + a + b + c = 1 + 2 + 0 + 1 = 4