Toán Lớp 8: (x-2)^3-(x-1)(x^2+x+1)+6x(x-1)=5
Leave a reply
Register Now
Login
Lost Password
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Toán Lớp 8: (x-2)^3-(x-1)(x^2+x+1)+6x(x-1)=5
Comments ( 2 )
Giải đáp:
(x-2)^3-(x-1)(x^2+x+1)+6x(x-1)=5
<=> x^3 – 6x^2 + 12x – 8 – x^3 + 1 + 6x^2 – 6x – 5 = 0
<=> ( x^3 – x^3 ) – ( 6x^2 – 6x^2) + ( 12x – 6x ) – ( 8 – 1 + 5)= 0
<=> 6x – 12 = 0
<=> 6x = 12
<=> x = 2
Vậy S={ 2}
Áp dụng:
1. ( A + B)^3 = A^3 – 3A^2 B + 3AB^2 – B^3
2. A^3 – B^3 = ( A – B)( A^2 + AB + B^2)
(x-2)^3-(x-1)(x^2+x+1)+6x(x-1)=5
⇒(x^3-3.x^2 .2+3.x .2^2-2^3)-(x^3-1)+6x^2-6x=5
⇒x^3-6x^2+12x-8-x^3+1+6x^2-6x=5
⇒(x^3-x^3)+(-6x^2+6x^2)+(12x-6x)+(-8+1)=5
⇒6x-7=5
⇒6x=12
⇒x=2
Vậy x=2