Toán Lớp 8: Bài 2: Rút gọn biểu thức:
a) B = (x + y)2 – 2(x + y)(x – y) + (x – y)2
= x2 + 2xy + y2 – 2×2 + 2y2 + x2 – 2xy + y2 = 4y2
b) C = (x + y)3 – (x – y)3 – 2y3
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: Bài 2: Rút gọn biểu thức:
a) B = (x + y)2 – 2(x + y)(x – y) + (x – y)2
= x2 + 2xy + y2 – 2×2 + 2y2 + x2 – 2xy + y2 = 4y2
b) C = (x + y)3 – (x – y)3 – 2y3
Comments ( 2 )
a)B = {\left( {x + y} \right)^2} – 2\left( {x + y} \right)\left( {x – y} \right) + {\left( {x – y} \right)^2}\\
= {\left( {x + y – \left( {x – y} \right)} \right)^2}\\
= {\left( {x + y – x + y} \right)^2}\\
= {\left( {2y} \right)^2}\\
= 4{y^2}\\
b)\\
C = {\left( {x + y} \right)^3} – {\left( {x – y} \right)^3} – 2{y^3}\\
= {x^3} + 3{x^2}y + 3x{y^2} + {y^3}\\
– \left( {{x^3} – 3{x^2}y + 3x{y^2} – {y^3}} \right) – 2{y^3}\\
= 6{x^2}y
\end{array}$