rút gọn biểu thức sau: a. 777775.777780.777773-777777.777772.777779 b. 888887.888892.888885-888889.888884.888891

0 bình luận về “rút gọn biểu thức sau: a. 777775.777780.777773-777777.777772.777779 b. 888887.888892.888885-888889.888884.888891”

1. $a)777775.777780.777773-777777.777772.777779$

   $=777775.(777775+5).(777775-2)-(777775+2).(777775-3).(777775+4)$

   $\text{Đặt 777775 = x, thì ta có:}$

   $⇒777775.(777775+5).(777775-2)-(777775+2).(777775-3).(777775+4)$

   $=x(x+5)(x-2)-(x+2)(x-3)(x+4)$

   $=x(x^2+3x-10)-(x^2-x-6)(x+4)$

   $=x^3+3x^2-10x-(x^3+4x^2-x^2-4x-6x-24)$

   $=x^3+3x^2-10x-x^3-4x^2+x^2+4x+6x+24$

   $=24.$

   $b)888887.888892.888885-888889.888884.888891$

   $=(888890-3).(888890+2).(888890-5)-(888890-1).(888890-6).(888890+1)$

   $\text{Đặt 888890 = y, thì ta có:}$

   $⇒(888890-3).(888890+2).(888890-5)-(888890-1).(888890-6).(888890+1)$

   $=(y-3)(y+2).(y-5)-(y-1)(y-6)(y+1)$

   $=(y^2+2y-3y-6)(y-5)-(y^2-1)(y-6)$

   $=(y^2-y-6)(y-5)-(y^2-1)(y-6)$

   $=y^3-5y^2-y^2+5y-6y+30-(y^3-6y^2-y+6)$

   $=y^3-5y^2-y^2+5y-6y-30-y^3+6y^2+y-6$

   $=24.$

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