Bài 1 : Rút gọn biểu thức sau a ) xy ( x^5 – y ³ ) – x ² y ( x^4 – y ³) b ) x ³ y^4 ( x ² – y ³ ) – x ² y ³ ( x^4 – y^4) c ) 90 . 10^n – 10^n+ ² + 10

$a)$

    $xy ( x^5 – y ³ ) – x ² y ( x^4 – y ³)$

$=x^6y-xy^4-x^6y+x^2y^4$

$=-xy^4+x^2y^4$

$b)$

     $x ³y^4(x²-y ³)-x ²y³(x^4-y^4)$

$=x^5y^4-x^3y^7-x^6y^3+x^2y^7$

$c)$

    $90.10^n-10^{n+2}+10^n+1$

$=900^n-10^{n+2}+10^n+1$

$d)$

    $y ( x^{n-1}+ y^{n-1} ) – x^{n-1} ( x + y )$

$=yx^{n-1}+y^n-x^n-x^{n-1}y$

$=y^n-x^n$

xin hay nhất ạ