Thực hiện phép tính: $a)(2x-1)(x^2+5-4)$ $b)-(5x-4)(2x+3)$ $c)7x(x-4)-(7x+3)(2x^2-x+4)$ 08/08/2021 Bởi Autumn Thực hiện phép tính: $a)(2x-1)(x^2+5-4)$ $b)-(5x-4)(2x+3)$ $c)7x(x-4)-(7x+3)(2x^2-x+4)$
\(\begin{array}{l}a)\,\left( {2x – 1} \right)\left( {{x^2} + 5 – 4} \right) = \left( {2x – 1} \right)\left( {{x^2} + 1} \right)\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 2{x^3} + 2x – {x^2} – 1\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \,2{x^3} – {x^2} + 2x – 1\end{array}\) \(\begin{array}{l}b)\, – \left( {5x – 4} \right)\left( {2x + 3} \right)\\ = \left( {4 – 5x} \right)\left( {2x + 3} \right)\\ = 8x + 12 – 10{x^2} – 15x\\ = – 10{x^2} – 7x + 12\end{array}\) \(\begin{array}{l}c)\,7x\left( {x – 4} \right) – \left( {7x + 3} \right)\left( {2{x^2} – x + 4} \right)\\ = 7{x^2} – 28x – 14{x^3} + 7{x^2} – 28x – 6{x^2} + 3x – 12\\ = – 14{x^3} + 8{x^2} – 53x – 12\end{array}\) Bình luận
Đáp án: a) (2x-1)(x² + 5 – 4) = 2x³ + 10x – 8x -x² -5 + 4 = 2x³ -x² + 2x -1 b) -(5x-4)(2x+3) = -( 10x² + 15x – 8x – 12) = -(10x² + 7x -12 ) = -10x² – 7x + 12 c) 7x(x-4) -(7x+3)(2x² – x + 4 ) = 7x²- 28x – (14x³ – 7x² +28x + 6x² – 3x + 12) = 7x² – 28x – (14x³ – x² + 25x + 12) = 7x² – 28x – 14x³ +x² – 25x – 12 = 7x³ + 8x² -53x -12 Bình luận
\(\begin{array}{l}a)\,\left( {2x – 1} \right)\left( {{x^2} + 5 – 4} \right) = \left( {2x – 1} \right)\left( {{x^2} + 1} \right)\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 2{x^3} + 2x – {x^2} – 1\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \,2{x^3} – {x^2} + 2x – 1\end{array}\)
\(\begin{array}{l}b)\, – \left( {5x – 4} \right)\left( {2x + 3} \right)\\ = \left( {4 – 5x} \right)\left( {2x + 3} \right)\\ = 8x + 12 – 10{x^2} – 15x\\ = – 10{x^2} – 7x + 12\end{array}\)
\(\begin{array}{l}c)\,7x\left( {x – 4} \right) – \left( {7x + 3} \right)\left( {2{x^2} – x + 4} \right)\\ = 7{x^2} – 28x – 14{x^3} + 7{x^2} – 28x – 6{x^2} + 3x – 12\\ = – 14{x^3} + 8{x^2} – 53x – 12\end{array}\)
Đáp án:
a) (2x-1)(x² + 5 – 4)
= 2x³ + 10x – 8x -x² -5 + 4
= 2x³ -x² + 2x -1
b) -(5x-4)(2x+3)
= -( 10x² + 15x – 8x – 12)
= -(10x² + 7x -12 )
= -10x² – 7x + 12
c) 7x(x-4) -(7x+3)(2x² – x + 4 )
= 7x²- 28x – (14x³ – 7x² +28x + 6x² – 3x + 12)
= 7x² – 28x – (14x³ – x² + 25x + 12)
= 7x² – 28x – 14x³ +x² – 25x – 12
= 7x³ + 8x² -53x -12