When f(x) is divided by x−1, the remainder is 12. When f(x) is divided by x−4, the remainder is 3 . Find the remainder when f(x) is divided by x2−5x+4.
Q. When f(x) is divided by x−1, the remainder is 12. When f(x) is divided by x−4, the remainder is 3 . Find the remainder when f(x) is divided by x2−5x+4.
Understand the Problem: Understand the problem.We are given that f(x) leaves a remainder of 12 when divided by x−1, and a remainder of 3 when divided by x−4. We need to find the remainder when f(x) is divided by (x−1)(x−4)=x2−5x+4.
Use the Remainder Theorem: Use the Remainder Theorem.The Remainder Theorem states that if a polynomial f(x) is divided by x−a, the remainder is f(a). We apply this theorem to the given information.For x−1: f(1)=12For x−4: f(4)=3
Express f(x): Express f(x) in terms of the divisors and remainders.Since we know the remainders when f(x) is divided by x−1 and x−4, we can express f(x) as:f(x)=(x−1)Q1(x)+12=(x−4)Q2(x)+3where Q1(x) and Q2(x) are some quotient polynomials.
Find Relationship: Find the relationship between Q1(x) and Q2(x).Since both (x−1)Q1(x)+12 and (x−4)Q2(x)+3 represent the same polynomial f(x), and the remainders are given for specific values of x, we can equate the two expressions for those values of x.For x=1: (1−1)Q1(1)+12=12For x=4: Q2(x)0This does not give us information about Q1(x) and Q2(x), but it confirms the remainders are correct.
Find Remainder: Find the remainder when f(x) is divided by (x−1)(x−4). We need to find a polynomial R(x) of degree less than 2 (since the divisor is a quadratic) such that: f(x)=(x2−5x+4)Q(x)+R(x) where Q(x) is the quotient polynomial and R(x) is the remainder polynomial we are looking for.
Use Given Remainders: Use the given remainders to determine R(x).Since R(x) must give the same remainders as f(x) for x=1 and x=4, we can set up a system of equations:R(1)=12R(4)=3Assuming R(x) is of the form ax+b, we can write:a(1)+b=12R(x)0
Solve Equations: Solve the system of equations for a and b. From the first equation, we get: a+b=12 From the second equation, we get: 4a+b=3 Subtracting the first equation from the second, we get: 3a=−9a=−3 Substituting a back into the first equation: −3+b=12b=15
Write Remainder Polynomial: Write down the remainder polynomial R(x). We found that a=−3 and b=15, so the remainder polynomial R(x) is: R(x)=−3x+15
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