Question

1) rút gọn các đẳng thức sau

a) (m+n)^2-(m-n)^2+(m+n)(m-n)

b) (a+b)^2-(a-b)^2-2a^3

c) (2x+1)^2+(2x-1)^2+2(4x^2-1)

d) (a+b+c)^2-2(a+b+c)^2(b+c)=(b=+c)^2

 

Answer 1

a) \(\cdot\left(m+n\right)^2-\left(m-n\right)^2+\left(m+n\right)\left(m-n\right)\)

\(=\left(m+n+m-n\right)\left(m+n-m+n\right)+\left(m+n\right)\left(m-n\right)\)

\(=\left(2m\cdot2n\right)+m^2-n^2\)

\(=4mn+m^2-n^2\)

b) \(\left(a+b\right)^2-\left(a-b\right)^2-2a^3\)

\(=\left(a+b+a-b\right)\left(a+b-a+b\right)-2a^3\)

\(=2ab-2a^3\)

c) \(\left(2x+1\right)^2+\left(2x-1\right)^2+2\left(4x^2-1\right)\)

\(=\left(2x+1\right)^2+2\left(2x+1\right)\left(2x-1\right)+\left(2x-1\right)^2\)

\(=\left(2x+1+2x-1\right)^2\)

\(=\left(4x\right)^2=16x^2\)

d) \(\left(a+b+c\right)^2-2\left(a+b+c\right)\left(b+c\right)+\left(b+c\right)^2\)

\(=\left(a+b+c-b-c\right)^2=a^2\)

Answer 2

xin lỗi mk ghi sai đề ở bài :d) (a+b+c)^2-2(a+b+c)(b+c)+(b+c)^2