十万里加急!!! 高中数学题!!!!! 求助 大神, 希望有高人 耐心指点, thx 希望 我能早早的 被 贵人 找到! 因为 本人 打速成 很慢, 所以都用 拼音。 求解下题 并 提供 列式, 列式,因为这很重要, 能解说一下更好?

2017-08-07 7:04 am
47. When a polynomial f(x) is divided by x-5, the remainder is 9. When f(x) is divided by x+2, the remainder is -5. Find the remainder when f(x) is divided by (x-5)(x+2). (model ans: 2x-1)

46. The remainder when a polynomial f(x) is divided by (x-2)(x+3) is ax+b. When f(x) is divided by x-2, the remainder is 5. x+3 is a factor of f(x). Find the values of a and b. (model ans: a=1, b=3)


45. It is given that x(2次方) + x - 6 is a factor of f(x) =x(3次方)+ax(2次方)-14x+b .
(a) Find the values of a and b. (model ans:a=-7, b=48)

(b) Factorize f(x). (model ans: (x-2)(x+3)(x-8) )

这题 重点 想问的是 (a) 部分, 我 是 用 非传统非正规(书中未教的法子)方法 侥幸 算出, 即 长除法。 因为 一般都是 给 linear factor, 但这次是给 quadratic factor: x(2次方)+x -6。 如何在 x(2次方)+x -6 身上 使用 factor theorem? 因为根据 书中所说,用 factor theorem 才是 正规方法。

43.(b) Factorize the following polynomials. 3x(3次方)+4x(2次方)-10x+4
(model ans: (3x-2)(x(2次方)+2x-2) )
这题 和上一题有点像, 不过方向好像是反过来的。如果我不先去求得 factor (3x-2), 怎 么先 从 3x(3次方) 和 4 中 抽出/ 先求出 (x(2次方)+2x-2)???

41. Let f(x) be a polynomial. When f(x) is divided by x+2, the quotient is 2x(2次方)-13x+18. It is given that x-5 is a factor of f(x). (a) Find f(x). (b)...(唔重要,难系难在(a)) (model ans: 2x(3次方)-9x(2次方)-8x+15)

这题无讲明 有无 remainder,够 怪鸡, 而 之后计算证明有 remainder, 但我又系用小小智慧 用非正规 法子 预计出 答案,正规法子系点? 关键系条式无太知点写。

回答 (1)

2017-08-07 6:57 pm
47. f(x) = (x - 5)Q(x) + 9. Put x = 5, f(5) = 9. f(x) = (x + 2)H(x) - 5. Put x = -2, f(-2) = -5.
f(x) = (x - 5)(x + 2)G(x) + ax + b. Put x = 5, f(5) = 5a + b = 9 ....(1) Put x = -2, f(-2) = -2x + b = - 5.....(2). Solve (1) and (2) get a = 2 and b = -1, so remainder is 2x - 1.
45. x^3 + ax^2 -14x + b = (x^2 + x - 6)Q(x) = (x + 3)(x - 2)Q(x). Put x = - 3
-27 +9a + 42 + b = 0 ....(1)
Put x = 2, 8 + 4a - 28 + b = 0 ....(2). Solve (1) and (2) get a= -7 and b = 48.
41. f(x) = (x + 2)(2x^2 + 13 + 18) + R (a constant because f(x) is divided by a linear factor) = 2x^3 - 9x^2 - 8x + 36 + R. Since (x - 5) is a factor of f(x), so when we put x = 5, remainder = 0, that is 2(5^3) - 9(5^2) - 8(5) + 36 + R = 0, so R = -21, therefore f(x) =2x^3 - 9x^2 - 8x + 15.


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