Câu hỏi : Vừa bằng hạt đỗ , ăn giỗ cả làng . Là con gì ?

Câu trả lời : Là con ruồi .

Let f(x)=(x−a)(x−b)(c−a)(c−b)+(x−b)(x−c)(a−b)(a−c)+(x−c)(x−a)(b−c)(b−a)−1f(x)=(x−a)(x−b)(c−a)(c−b)+(x−b)(x−c)(a−b)(a−c)+(x−c)(x−a)(b−c)(b−a)−1

We have:

  f(a)=0+1+0−1=0f(a)=0+1+0−1=0

Similarity f(b)=0,f(c)=0f(b)=0,f(c)=0

f(x) is a degree of 2 and have 3 different solotutions (a, b, c) .

=> f(x) = 0

=> (x−a)(x−b)(c−a)(c−b)+(x−b)(x−c)(a−b)(a−c)+(x−c)(x−a)(b−c)(b−a)=1

Let f(x)=(x−a)(x−b)(c−a)(c−b)+(x−b)(x−c)(a−b)(a−c)+(x−c)(x−a)(b−c)(b−a)−1f(x)=(x−a)(x−b)(c−a)(c−b)+(x−b)(x−c)(a−b)(a−c)+(x−c)(x−a)(b−c)(b−a)−1

We have:

  f(a)=0+1+0−1=0f(a)=0+1+0−1=0

Similarity f(b)=0,f(c)=0f(b)=0,f(c)=0

f(x) is a degree of 2 and have 3 different solotutions (a, b, c) .

=> f(x) = 0

=> (x−a)(x−b)(c−a)(c−b)+(x−b)(x−c)(a−b)(a−c)+(x−c)(x−a)(b−c)(b−a)=1                                                             Study Well !