Question

1.已知x+3y=10,求(x^2-9y^2)/(x-3y)的值.

Answer 1

1.(x^2-9y^2)/(x-3y) =(x-3y)(x+3y)/(x-3y) =x+3y =10 2.a^2(a-3)-(a-3) =(a^2-1)(a-3) =(a-1)(a+1)(a-3) 3.根据题意得:x^2-5x-6=(x+1)(x-6) 即:m=6 4.4a^2+4a+b^2-6b+10=0 (4a^2+4a+1)-1+(b^2-6b+9)-9+10=0 (2a+1)^2-1+(b-3)^2-9+10=0 (2a+1)^2+(b-3)^2=0 (2a+1)^2=0 a=-1/2 (b-3)^2=0 b=3 a^3b-ab^3 =ab(a^2-b^2) =ab(a-b)(a+b) =(-1/2)*3*(-1/2-3)*(-1/2+3) =(-3/2)*(-7/2)*(5/2) =105/8 5.m^2-4mn+4n^2=0 (m-2n)^2=0 m=2n (m^2+n^2)/mn =[(2n)^2+n^2]/(2n*n) =(4n^2+n^2)/2n^2 =5n^2/2n^2 =5/2