已知a+5b=6,求a2（平方）+5ab+30b
答:原式=a(a+5b)+30b=a*6+30b=6(a+5b)=6*6=36
2.若3x2（平方）-x=1,則6x³+7x2（平方）-5x+2003
答:3x^2=x+1
原式=2x*(x+1)+7x^2-5x+2003
=2x^2+2x+7x^2-5x+2003
=9x^2+2x-5x+2003
=3(x+1)-3x+2003
=3+2003
=2006.
你題目中的"-5"后面應(yīng)該是"-5x"吧?
a=200x+2001,b=200x+2002,c=200x+2003
∴a-b=-1,b-c=-1,c-a=2
∴a2+b2+c2-ab-ac-bc
=1/2[2a2+2b2+2c2-2ab-2ac-2bc]
=1/2[（a-b)^2+(b-c)^2+(c-a)^2]
=1/2[（-1)^2+(-1)^2+2^2]
=3