Đáp án:
1) A=-7
Giải thích các bước giải:
\(\begin{array}{l}
1)A = x(x + 1) - {(x + 2)^2} = {x^2} + x - {x^2} - 4x - 4\\
= - 3x - 4\\
Thay:x = 1\\
\to A = - 3 - 4 = - 7\\
2)B = \left( {5x + 2} \right)\left( {2x - 7} \right) - \left( {2x + 5} \right)\left( {2x - 5} \right)\\
= 10{x^2} - 35x + 4x - 14 - 4{x^2} + 10x - 10x + 25\\
= 6{x^2} - 31x + 11\\
Thay:x = - 3\\
\to B = 6.9 - 31.\left( { - 3} \right) + 11 = 158\\
3)C = {(x - 2)^2} - (x - 3)(x + 3)\\
= {x^2} - 4x + 4 - {x^2} + 9\\
= - 4x + 13\\
Thay:x = 2\\
\to C = - 8 + 13 = 5\\
4)D = {(2x - 3)^3} + (4x + 1)(16{x^2} + 4x + 1)\\
= 8{x^3} - 3.4{x^2}.3 + 3.2x.9 - 27 + 64{x^3} + 16{x^2} + 16{x^2} + 4x + 4x + 1\\
= 72{x^3} - 4{x^2} + 62x - 26\\
5)E = {(3x + y)^3} - (x + 2y)({x^2} - 2xy + 4{y^2})\\
= {(3x + y)^3} - \left( {x + 2y} \right){\left( {x - 2y} \right)^2}\\
= 27{x^3} + 3.9{x^2}.y + 3.3x.{y^2} + {y^3} - \left( {{x^2} - 4{y^2}} \right)\left( {x - 2y} \right)\\
= 27{x^3} + 3.9{x^2}.y + 3.3x.{y^2} + {y^3} - {x^3} + 2{x^2}y + 4x{y^2} - 8{y^3}\\
= 26{x^3} + 29{x^2}y + 13x{y^2} - 7{y^3}
\end{array}\)
