Question

Xét biểu thức :                                                                                                          

P = 3x(4x-11) + 5x²(x-1) - 4x(3x+9) + x(5x-5x²⁾

^{a) Rút gọn P} 

^{b) Tính P khi x = 2}

^{c) Tìm x để P = 207}

Answer 1

a)Ta có:  P = 3x(4x - 11) + 5x²(x - 1) - 4x(3x + 9) + x(5x - 5x²)

P = 12x² - 33x + 5x³ - 5x² - 12x² - 36x + 5x² - 5x³

P = -69x

b) Ta có: x = 2

=> P = -69.2 = -138

c) Ta có: P = 207

=> -69x = 207

=> x = 207 : (-69)

=>  x = -3

Answer 2

\(a,P=3x\left(4x-11\right)+5x^2\left(x-1\right)-4x\left(3x+9\right)+x\left(5x-5x^2\right)\)

\(=12x^2-33x+5x^3-5x^2-12x^2-36x+5x^2-5x^3\)

\(=\left(12x^2-5x^2-12x^2+5x^2\right)-\left(33x+36x\right)+\left(5x^3-5x^3\right)\)

\(=-33x-36x=-69x\)

\(b,\)Khi \(x=2\Leftrightarrow P=-69.2=-138\)

\(c,\)Để \(P=207\Leftrightarrow-69x=207\Leftrightarrow x=-3\)