第1个回答 2009-03-27
(1)5(3a-2b)^2-2(2a+3b)^2-3(2b-3a)^2+4(3b+2a)^2
=5(3a-2b)^2-3(3a-2b)^2+4(3b+2a)^2 -2(2a+3b)^2
=2(3a-2b)^2+2(2a+3b)^2
=2(9a²-12ab+4b²)+2(4a²+12ab+9b²)
=18a²+8b²+8a²+9b²=26a^2+26b^2
答案:26a^2+26b^2
(2)[a-(1/2)]^2[a^2+(1/4)]^2[a+(1/2)]^2
=[a²-(1/2)²]^2[a^2+(1/2)²]^2
=[a^4-(1/2)^4]^2=a^8-(1/8)a^4+(1/256)
答案:a^8-(1/8)a^4+(1/256)
(3)[(-3/4)x^6y^3+(6/5)x^3y^4-(9/10)xy^5]÷(3/5)xy^3
=(-5/4)x^5+2x^2y-(3/2)y^2
答案:(-5/4)x^5+2x^2y-(3/2)y^2
(4)已知y=ax^5+bx^3+cx-2,当x=-3时,y=4,那么当x=3时,求y的值。
解:
4=a(-3)^5+b(-3)^3-3c-2
6=-3c-(243a+27b)
(243a+27b)=-3C-6
当x=3时
y=3c+(243a+27b)=3C-3C-6,Y=-6
答案:-8