b.
, a^4(b-c)+b^4(c-a)+c^4(a-b)
= a^4(b-c)-b^4[(b-c)+(a-b)]+c^4(a-b)
= (b -c) (a^4- b^4)+(a - b) (c^4- b^4)
= (b-c)(a^2-b^2)(a^2+b^2)+(a-b)(c^2-b^2)(c^2+b^2)
= (b-c)(a-b)(a+b)(a^2+b^2)-(a-b)(b-c)(b+c)(b^2+c^2) = (b-c)(a-b)(a^3+ab^2+ba^2+b -bc^2-b^3-cb^2-c^3)
= (b-c)(a-b)(a^3+ab^2+ba^2-bc^2-c^3-cb^2)
= (b-c)(a-b)(a^3-c^3)+b^2(a-c)+b(a^2-c^2)
= (b-c)(a-b)(a-c)(a^2+ac+c^2)+b^2(a-c)+b(a-c)(a+c)
= (b-c)(a-b)(a-c)(a^2+ac+c^2+b^2+ab+ac)
= (a-b)(b-c)(c-a)(a^2+b^2+c^2+ab+bc+ca)
c. Đặt x^2-x+1=a có
Đề bài = a(a+1)-20= a^2+a+1/4 - 81/4= (a+1/2)^2-(9/2)^2= (a+1/2-9/2)(a+1/2+9/2)=(a-4)(a+5) giờ thay x^2-x+1=a trở lại là có dcpcm nhé
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câu a ngại gõ quá tý có bn khác giúp
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