Bài làm:
Ta có: \(\left(2x+5\right)\left(x-2\right)-3\left(x+2\right)^2+\left(x+1\right)^2\)
\(=2x^2+x-10-3\left(x^2+4x+4\right)+x^2+2x+1\)
\(=3x^2+3x-9-3x^2-12x-12\)
\(=-9x-21\)
\(\left(2x+5\right)\left(x-2\right)-3\left(x+2\right)^2+\left(x+1\right)^2\)
\(=2x\left(x-2\right)+5\left(x-2\right)-3\left(x^2+4x+4\right)+\left(x^2+2x+1\right)\)
\(=2x^2-4x+5x-10-3x^2-12x-12+x^2+2x+1\)
\(=\left(2x^2-3x^2+x^2\right)+\left(5x-4x-12x+2x\right)-\left(10+12-1\right)\)
\(=0+x-10x-21=-9x-21\)
\(\left(2x+5\right)\left(x-2\right)-3\left(x+2\right)^2+\left(x+1\right)^2\)
\(=2x^2-4x+5x-10-3x^2-12x-12+x^2+2x+1\)
\(=-9x-21\)
( 2x + 5 )( x - 2 ) - 3( x + 2 )2 + ( x + 1 )2
= 2x2 + x - 10 - 3( x2 + 4x + 4 ) + x2 + 2x + 1
= 2x2 + x - 10 - 3x2 - 12x - 12 + x2 + 2x + 1
= -9x - 21
