Đề bài
Rút gọn các biểu thức sau:
a) \((x + 3)(x - 2) + {(x - 3)^2}\) ;
b) \({(x + 2)^2} + (x + 1)(x - 1)\) ;
c) \((2x - 1)(2x + 1) - {(2x - 3)^2}\) ;
d) \({(x + 2)^3} - {(x + 1)^3} - {(x + 1)^2}\).
Lời giải chi tiết
\(\eqalign{ & a)\,\,\left( {x + 3} \right)\left( {x - 2} \right) + {\left( {x - 3} \right)^2} \cr & \,\,\,\,\, = {x^2} - 2x + 3x - 6 + {x^2} - 6x + 9 \cr & \,\,\,\,\, = 2{x^2} - 5x + 3 \cr & b)\,\,{\left( {x + 2} \right)^2} + \left( {x + 1} \right)\left( {x - 1} \right) \cr & \,\,\,\,\, = {x^2} + 4x + 4 + {x^2} - 1 \cr & \,\,\,\,\, = 2{x^2} + 4x + 3 \cr & c)\,\,\left( {2x - 1} \right)\left( {2x + 1} \right) - {\left( {2x - 3} \right)^2} \cr & \,\,\,\,\, = {\left( {2x} \right)^2} - 1 - \left( {4{x^2} - 12x + 9} \right) \cr & \,\,\,\,\, = 4{x^2} - 1 - 4{x^2} + 12x - 9 \cr & \,\,\,\,\, = 12x - 10 \cr & d)\,\,{\left( {x + 2} \right)^3} - {\left( {x + 1} \right)^3} - {\left( {x + 1} \right)^2} \cr & \,\,\,\,\, = {x^3} + 6{x^2} + 12x + 8 - \left( {{x^3} + 3{x^2} + 3x + 1} \right) - \left( {{x^2} + 2x + 1} \right) \cr & \,\,\,\,\, = {x^3} + 6{x^2} + 12x + 8 - {x^3} - 3{x^2} - 3x - 1 - {x^2} - 2x - 1 \cr & \,\,\,\,\, = 2{x^2} + 7x + 6 \cr} \)
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