Bài `3` :
`a) A = 7x(x - 5) + 3(x - 2)`
`= 7x^2 - 35x + 3x - 6`
`= 7x^2 - 32x - 6`
`= 7 . 0^2 - 32.0 - 6`
`= -6`
`b) B = 4x ( 2x - 3) - 5x ( x - 2)`
`B = 8x^2 - 12x - 5x^2 + 10x`
`B = 3x^2 - 2x`
`B = 3.2^2 - 2.2 = 8`
`c) C = a^2(a + b) - b(a^2 - b^2) + 2013`
`C = a^3 + a^2b - ba^2 + b^3 + 2013`
`C = 1^3 + 1^2.(-1) - (-1) . 1 + (-1)^3 + 2013`
`C = 1 - 1 + 1 - 1 + 2013`
`C = 2013`
`d) D = m ( m - n + 1) - n(n + 1 - m)`
`D = m^2 - mn + m - n^2 - n + nm`
`D = (-2/3)^2 - (-2/3).(-1/3) + (-2/3) - (-1/3)^2 - (-1/3) + (-1/3) . (-2/3)`
`D = 0`
