Question

[Ran Mori]

Chứng minh các biểu thức sau viết đc dưới dạng tổng các bình phương 

\(x^2+2\left(x+1\right)^2+3\left(x+2\right)^2+4\left(x+3\right)^2\)

Answer 1

[Không Tên]

\(x^2+2\left(x+1\right)^2+3\left(x+2\right)^2+4\left(x+3\right)^2\)

\(=x^2+2\left(x^2+2x+1\right)+3\left(x^2+4x+4\right)+4\left(x^2+6x+9\right)\)

\(=10x^2+40x+50\)

\(=\left(x^2+10x+25\right)+\left(9x^2+30x+25\right)\)

\(=\left(x+5\right)^2+\left(3x+5\right)^2\)

Answer 2

[Mai Thanh Xuân]

\(x^2+2\left(x+1\right)^2+3\left(x+2\right)^2+4\left(x+3\right)^2\)

\(=x^2+2\left(x^2+2x+1\right)+3\left(x^2+4x+4\right)+4\left(x^2+6x+9\right)\)

\(=x^2+2x^2+4x+2+3x^2+12x+12+4x^2+24x+36\)

\(=10x^2+40x+50\)

\(=\left(9x^2+30x+25\right)+\left(x^2+10x+25\right)\)

\(=\left(3x+2\right)^2+\left(x+5^2\right)\)