Đáp án:
Giải thích các bước giải:
Bài 38 :
`1) x^2 +4x+4`
`=x^2 +2.x.2 +2^2`
`=(x+2)^2`
`2)16-8x+x^2`
`=4^2 -2.x.4 +x^2`
`=(4-x)^2`
`3)x^2 +6xy +9y^2`
`=x^2 +2.x.3y +(3y)^2`
`=(x+3y)^2`
Bài 39 :
`1) 1+3x +3x^2 +x^3`
`=1^3 +3.x.1^2 +3x^2 .1 +x^3`
`=(1+x)^3`
`2)x^3 -12x^2 +48x -64`
`=x^3 -3.x^2 .4 + 3.x.16 -4^3`
`=x^3 -3.x^2 .4 +3.x.4^2 -4^3`
`=(x-4)^3`
`3)x^3 -6x^2 +12x -8`
`=x^3 -3.x^2 .2 +3.x^2 .4 -2^3`
`=x^3 -3.x^2 .2 +3.x^2 .2^2 -2^3`
`=(x-2)^3`
Bài 40 :
`1)x^2 -64`
`=x^2 -8^2`
`=(x-8)(x+8)`
`2)a^2 -9b^2`
`=a^2 - (3b)^2`
`=(a-3b)(a+3b)`
`3)(x+3)^2 - 16`
`=(x+3)^2 -4^2`
`=(x+3-4)(x+3+4)`
