Bài 1:Thực hiện phép nhân sau a, 2x.(3x+2x) b,5x^2.(x+2x) c,4x.(x^2-3x+4) d,-7x^3.(x^2-2x-3) e,(x+1).(x-3) f,(3x-2).(3x+2) g,

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1. Giải đáp:

   a, 2x.(3x+2x) = 2x.5x = 10x^2

   b, 5x^2.(x+2x) = 5x^2.3x = 15x^3

   c, 4x.(x^2-3x+4) = 4x^3 – 12x^2 + 16x

   d, -7x^3.(x^2-2x-3) = -7x^5 + 14x^4 + 21x^3

   e, (x+1).(x-3) = x^2 – 2x – 3

   f, (3x-2).(3x+2) = 9x^2 – 4

   g, (5-x).(5+x) = 25 – x^2

   h, (3x-1).(1-3x) = -9x^2 + 3x + 1

   k, (3+x).(9-3x+x^2) = 9x – 3x^2 + 3x^2 + x^3 = x^3 + 6x

   e, (2x-4).(x^2+2x+4) = 2x^3 + 4x^2 – 8x^2 – 16x + 8x + 16 = 2x^3 – 4x^2 + 8x + 16

   m, (4x+5).(2x-4) = 8x^2 – 16x + 10x – 20 = 8x^2 – 6x – 20.

   Trả lời
2. a)$2x(3x+2x)$

   $=2x.5x$

   $=10x^2$

   b)$5x^2(x+2x)$

   $=5x^2.3x$

   $=15x^3$

   c)$4x(x^2-3x+4)$

   $=4x.x^2-4x.3x+4x.4$

   $=4x^3-12x^2+16x$

   d)$-7x^3(x^2-2x-3)$

   $=-7x^3.x^2-(-7x^3.-2x)-(-7x^3.-3)$

   $=-7x^5-(14x^4)-(21x^3)$

   $=-7x^5-14x^4-21x^3$

   e)$(x+1)(x-3)$

   $=x.x+x.-3+1.x+1.-3$

   $=x^2-3x+1x-3$

   $=x^2-2x-3$

   f)(3x-2)(3x+2)

   $=3x.3x+3x.2-2.3x-2.2$

   $=9x^2+6x-6x-4$

   $=9x^2-4$

   g)$(5-x)(5+x)$

   $=5.5+5.x-x.5-x.x$

   $=25+5x-5x-x^2$

   $=25-x^2$

   $=-x^2+25$

   h)$(3x-1)(1-3x)$

   $=3x.1+3x.-3x-1.1-1.-3x$

   $=3x-9x^2-1+3x$

   $=-9x^2+6x-1$

   k)$(3+x)(9-3x+x^2)$

   $=3.9+3.-3x+3.x^2+x.9+x.-3x+x.x^2$

   $=27-9x+3x^2+9x-3x^2+x^3$

   $=x^3+27$

   e)$(2x-4)(x^2+2x+4)$

   $=2x.x^2+2x.2x+2x.4-4.x^2-4.2x-4.4$

   $=2x^3+4x^2+8x-4x^2-8x-16$

   $=2x^3-16$

   m)$(4x+5)(2x-4)$

   $=4x.2x+4x.-4+5.2x+5.-4$

   $=8x^2-16x+10x-20$

   $=8x^2-6x-20$

   $\text{mong mình đc ctlhn :<}$

   Trả lời