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If x + 1 and x-1 ghe factors of f (x) = x ^ 3 + 2ax + b calculate the valves of a and b. using theses values of and by factorise f(x) completely.​

User Juanker
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1 Answer

8 votes
8 votes

Since both x + 1 and x - 1 are factors of f(x), we have the factorization

x³ + 2ax + b = (x + 1) (x - 1) (x - b)

where the last root must be x = b in order that b is the constant term in the cubic.

Expanding the right side and equating coefficients gives

x³ + 2ax + b = x³ - bx² - x + b

which tells us

-b = 0 ⇒ b = 0

2a = -1 ⇒ a = -1/2

Then we have

f(x) = x³ + 2 (-1/2) x + b = x³ - x

or

f(x) = x (x + 1) (x - 1)

User Ashish Musale
by
3.1k points
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