Toán Lớp 8: Bài 1:thực hiện phép tính sau đây a)(x^2-1)(x^2+2x) b)(2x-1)(3x+2)(3-x) c)(x+3)(x^2+3x-5) d)(x+1)(x^2-x+1) e)(2x^3-3x-1).(5

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Toán Lớp 8:  Bài 1:thực hiện phép tính sau đây a)(x^2-1)(x^2+2x)      b)(2x-1)(3x+2)(3-x)    c)(x+3)(x^2+3x-5)    d)(x+1)(x^2-x+1)  e)(2x^3-3x-1).(5x+2)   f)(x^2-2x+3).(x-4)

thanhbinh2k5 · Answer

Giải đáp+Lời giải và giải thích chi tiết:          B&agrave;i 1:       a) (x&sup2;-1).(x&sup2;+2x)     = x&sup2;.x&sup2;+x&sup2;.2x-1.x&sup2;-1.2x     = x^4+2x&sup3;-x&sup2;-2x     b) (2x-1).(3x+2).(3-x)     = (6x&sup2;+4x-3x-2).(3-x)     = (6x&sup2;+x-2).(3-x)     =6x&sup2;.3-6x&sup2;.x+x.3-x.x-2.3+2.x     = 18x&sup2;-6x&sup3;+3x-x&sup2;-6+2x     = (18x&sup2;-x&sup2;)-6x&sup3;+(3x+2x)-6     = -6x&sup3;+17x&sup2;+5x-6     c) (x+3).(x&sup2;+3x-5)     = x.x&sup2;+x.3x-x.5+3.x&sup2;+3.3x-3.5     =x&sup3;+3x&sup2;-5x+3x&sup2;+9x-15     = x&sup3;+(3x&sup2;+3x&sup2;)+(9x-5x)-15     = x&sup3;+6x&sup2;+4x-15     d) (x+1).(x&sup2;-x+1)     = x.x&sup2;-x.x+x.1+1.x&sup2;-1.x+1.1     = x&sup3;-x&sup2;+x+x&sup2;-x+1     = x&sup3;+[(-x&sup2;)+x&sup2;]+(x-x)+1     = x&sup3;+1     e) (2x&sup3;-3x-1).(5x+2)     = 2x&sup3;.5x+2x&sup3;.2-3x.5x-3x.2-1.5x-1.2     = 10x^4+4x&sup3;-15x&sup2;-6x-5x-2     = 10x^4+4x&sup3;-15x&sup2;-(6x+5x)-2     = 10x^4+4x&sup3;-15x&sup2;-11x-2     f) (x&sup2;-2x+3).(x-4)     = x&sup2;.x-x&sup2;.4-2x.x+2x.4+3.x-3.4     =x&sup3;-4x&sup2;-2x&sup2;+8x+3x-12     = x&sup3;-(4x&sup2;+2x&sup2;)+(8x+3x)-12     = x&sup3;-6x&sup2;+11x-12       Ch&uacute;c bạn hc tốt!         @Applesff