Tìm giá trị lớn nhất của biểu thức:
M=(x-5)(x+1)-2(x+7)(x-2)+2(7x-1)
=x2+x-5x-5-2(x2+2x-7x-14)+14x-2
=x2+x-5x-5-2x2+4x-14x-28+14x-2
=-x2+4x-35
N=x2(1-x)(1+x)-2(x-2)(x+3)-2(3-x)
=x2(1-x2)-2(x2+3x-2x-6)-6+2x
=x2-x4-2x2-2x+12-6+2x
=-x2-x4+6
M = (x-5) (x+1)-2(x+7)(x-2)+2(7x-1)
M = x2+ x - 5x - 5 - (2x-14).(x- 2) + 14x - 2
M = x2+ x - 5x -5 - 2x2 - 4x -14x + 28 + 14x - 2
M = -x2 - 8x - 7
N = x2(1 - x) - 2 (x - 2) (x+ 3) - 2(3 - x)
N = x4 + x2 + 12 - 2 x2 - 6 + 2x
N = x2(1 - x) - 2 (x - 2) (x+ 3) - 2(3 - x)
N = x4 + x2 + 12 - 2 x2 - 6 + 2x
N = x4 - x2 + 6 + 2x
bài kia thiếu nha mấy bạn
\(M=\left(x-5\right)\left(x+1\right)-2\left(x+7\right)\left(x-2\right)+2\left(7x-1\right)\)
\(=x^2-4x-5-2\left(x^2+5x-14\right)+14x-2\)
\(=x^2+10x-7-2x^2-10x+28\)
\(=-x^2+21< =21\)
Dấu '=' xảy ra khi x=0
