Question

化简求值:x/[9(x-y)^2]*[(x^2-y^2)/(x+y)]+{[(x^2+2)/(x+y)]-2}

Answer 1

1、

x/9(x-y)^2 *(x-y)+(x^2+2-x-y)/(x+y)

=x/9(x-y)+(x^2+2)/(x+y)-2

=[(x(x+y)+9(x-y)(x^2+2)]/9(X-Y)(X+Y)-2

=[X^2+XY+9X^3+18X-9X^2Y-18XY]/9(X^2-Y^2)-2

=[X(9X^2+X+18)+XY(9X-7)]/9(X^2-Y^2)-2

2、

X

(X+c)*t=a

(X-c)*t=b

(X+c)/(X-c)=a/b

aX-ac=bX+bc

c(a+b)=X(b-a)

X=c(a+b)/(b-a)

即为所求船在静水中的速度