Question

已知代数式2x^2+ax-y+6-2bx^2+503x-5y-1的值与字母x的取值无关,A=4a^2-ab+4b^2,B

Answer 1

∵代数式2x^2+ax-y+6-2bx^2+503x-5y-1的值与字母x的取值无关

∴2-2b=0且a+503=0

∴a= -503,b=1

3A-4B

=3(4a^2-ab+4b^2)-4(3a^2-ab+3b^2)

=12a^2-3ab+12b^2-12a^2+4ab-12b^2

=ab

= -503