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question:Given the polynomial f(x) = a_{0} x^{n} + a_{1} x^{n1} + cdots + a_{n1} x + a_{n} where the coefficients a_{0}, a_{1}, cdots, a_{n} are all integers, and both f(2) and f(3) are divisible by 6. Prove that f(5) is also divisible by 6.

answer:1. Let us recall the given polynomial function: [ f(x) = a_{0} x^{n} + a_{1} x^{n-1} + cdots + a_{n-1} x + a_{n} ] We are given that (f(x)) has integer coefficients (a_{0}, a_{1}, ldots, a_{n}) and both (f(2)) and (f(3)) are divisible by 6. 2. Starting with the evaluations: [ f(2) = a_{0} 2^{n} + a_{1} 2^{n-1} + cdots + a_{n-1} 2 + a_{n} ] and [ f(3) = a_{0} 3^{n} + a_{1} 3^{n-1} + cdots + a_{n-1} 3 + a_{n} ] 3. Since (f(2)) is divisible by 6, it must be divisible by both 2 and 3 individually. - From (f(2)) being divisible by 2, every term except the constant term (a_{n}) contains at least one factor of 2 (since they are powers of 2). This implies that (a_{n}) must be divisible by 2. - Similarly, from (f(3)) being divisible by 3, every term except the constant term (a_{n}) contains at least one factor of 3 (since they are powers of 3). This implies that (a_{n}) must be divisible by 3. 4. Since (a_{n}) is divisible by both 2 and 3, it must be divisible by their least common multiple, which is 6. 5. We now analyze the divisibility of (f(5)): [ f(5) = a_{0} (2+3)^{n} + a_{1} (2+3)^{n-1} + cdots + a_{n-1} (2+3) + a_{n} ] 6. Using the binomial theorem to expand ((2+3)^{k}): [ f(5) = a_{0} sum_{k=0}^{n} binom{n}{k} 2^{k} 3^{n-k} + a_{1} sum_{k=0}^{n-1} binom{n-1}{k} 2^{k} 3^{n-1-k} + cdots + a_{n-1} sum_{k=0}^{1} binom{1}{k} 2^{k} 3^{1-k} + a_{n} ] 7. Combining the given information: [ f(5) = f(2) + f(3) - a_{n} + a_{0} left(C_{n}^{1} 2^{n-1} cdot 3 + C_{n}^{2} 2^{n-2} cdot 3^{2} + cdots + C_{n}^{n-1} 2 cdot 3^{n-1} right) ] [ + a_{1} left(C_{n-1}^{1} 2^{n-2} cdot 3 + C_{n-1}^{2} 2^{n-3} cdot 3^{2} + cdots + C_{n-1}^{n-2} 2 cdot 3^{n-2} right) ] [ + cdots + a_{n-2} cdot C_{2}^{1} cdot 2 cdot 3 ] 8. Reviewing each term, we observe that every term contains a multiples of 6 and thus (f(5)) must be divisible by 6 as each term remains divisible by 6. 9. Conclusion: [ f(5) text{ is divisible by } 6. ] [ boxed{6} ]

question:Given that the graph of the power function f(x) passes through the point (3, frac{1}{9}), find f(2)= _____.

answer:Since the graph of the power function f(x)=x^{a} passes through the point (3, frac{1}{9}), we have 3^{a}= frac{1}{9}, solving for a gives a=-2. Hence, f(x)=x^{-2}, and f(2)=(2)^{-2}= frac{1}{4}. Therefore, the answer is: boxed{frac{1}{4}}. We deduce f(x)=x^{-2} from the given conditions, from which we can find the value of f(2). This problem tests the method of finding function values and is a basic question. When solving, carefully read the question and pay attention to the reasonable application of function properties.

question:Three faces of a right rectangular prism have areas of 60, 70, and 84 square units. What is the volume of the prism, in cubic units? Express your answer to the nearest whole number.

answer:Let (a), (b), and (c) be the dimensions of the prism, such that (ab=60), (bc=70), and (ca=84). We are tasked with finding the volume (abc). Start by multiplying the equations for the areas: [ (ab)(bc)(ca) = 60 cdot 70 cdot 84. ] This simplifies to: [ a^2b^2c^2 = 60 cdot 70 cdot 84. ] Taking the square root of both sides gives: [ abc = sqrt{60 cdot 70 cdot 84}. ] Breaking down the numbers into prime factors, we get: [ 60 = 2^2 cdot 3 cdot 5, quad 70 = 2 cdot 5 cdot 7, quad 84 = 2^2 cdot 3 cdot 7. ] Thus, [ abc = sqrt{(2^2 cdot 3 cdot 5) cdot (2 cdot 5 cdot 7) cdot (2^2 cdot 3 cdot 7)} = sqrt{2^5 cdot 3^2 cdot 5^2 cdot 7^2}. ] Simplifying further, [ abc = 2^{5/2} cdot 3 cdot 5 cdot 7 = 4 cdot sqrt{2} cdot 3 cdot 5 cdot 7 = 420 sqrt{2}. ] Rounding to the nearest whole number gives: [ abc approx 420 cdot 1.414 = 593.88 approx boxed{594} text{ cubic units}. ]

question:Find the units digit of the decimal expansion of [left(7 + sqrt{50}right)^{21} + left(7 sqrt{50}right)^{21}.] textbf{(A)} 2qquad textbf{(B)} 4qquad textbf{(C)} 5qquad textbf{(D)} 7qquad textbf{(E)} text{none of these}

answer:1. **Define the Expressions**: Let C = 7 + sqrt{50} and D = 7 - sqrt{50}. 2. **Application of Conjugate Properties**: As C and D are conjugates, their expansions help simplify, especially using the binomial theorem: [ C^{21} + D^{21} = 2left[binom{21}{0}7^{21} + binom{21}{2}7^{19}50 + cdotsright] ] 3. **Focusing on Units Digit**: Consider units digit calculations using modular 10 arithmetic: - Since 7^{21} modulo 10 needs to be calculated, remember (7^2 equiv 49 equiv -1 pmod{10}). Thus, 7^4 equiv 1pmod{10} and hence 7^{21} equiv 7 times (7^4)^5 equiv 7 times 1^5 equiv 7 pmod{10}. 4. **Other Higher Power Terms**: Consider the higher powers terms such as binom{21}{2}7^{19}50 pmod{10}, but recall all even powers of sqrt{50} become 50 with some power, reducing modulo 10 still results in 0, simplifying contribution calculations. 5. **Summarize All Contributions**: [ (C^{21} + D^{21}) pmod{10} = 2 times 7 equiv 14 equiv 4 pmod{10} ] Thus, the units digit of C^{21} + D^{21} is 4. The final answer is boxed{textbf{(B)} 4}

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