Toán Lớp 8: bài 1:Phân tích đa thức thành nhân tử chung a)36-12x+x^2 b)4x^2+12x+9 c)-25x^6-y^8+10x^3y^4 d)1/4x^2-5xy+25y^2 e)(x-5)^2-16 f)25-(3-x)^

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Toán Lớp 8:  bài 1:Phân tích đa thức thành nhân tử chung a)36-12x+x^2 b)4x^2+12x+9 c)-25x^6-y^8+10x^3y^4 d)1/4x^2-5xy+25y^2 e)(x-5)^2-16 f)25-(3-x)^2 g)(7x-4)^2-(2x+1)^2 h)8x^3+1/27 i)125-x^8 LÀM HỘ TUI

minhtuyethue · Answer

Giải đáp+Lời giải và giải thích chi tiết:         B&agrave;i 1:      a) 36-12x+x^2   =x^2-2.x.6+6^2   =(x-6)^2   b) 4x^2+12x+9   =(2x)^2+2.2x.3+3^2   =(2x+3)^2   c) -25x^6-y^8+10x^3y^4   =-(25x^6-10x^3y^4+y^8)   =-[(5x^3)^2-2.5x^3 .y^4+(y^4)^2]   =-(5x^3-y^4)^2   d) 1/4x^2-5xy+25y^2   =(1/2x)^2-2. 1/2x . 5y +(5y)^2   =(1/2x-5y)^2   e) (x-5)^2-16   =(x-5)^2-4^2   =[(x-5)-4].[(x-5)+4]   =(x-5-4).(x-5+4)   =(x-9).(x-1)   f) 25-(3-x)^2   =5^2-(3-x)^2   =[5-(3-x)].[5+(3-x)]   =(5-3+x).(5+3-x)   =(2+x).(8-x)   g) (7x-4)^2-(2x+1)^2   =[(7x-4)-(2x+1)].[(7x-4)+(2x+1)]   =(7x-4-2x-1)(7x-4+2x+1)   =(5x-5).(9x-3)   =5.(x-1).3.(3x-1)   =15(x-1)(3x-1)   h) 8x^3+1/(27)   =(2x)^3+(1/3)^3   =(2x+1/3).[(2x)^2-2x . 1/3 +(1/3)^2]   =(2x+1/3).(4x^2-2/3x+1/9)   i) 125-x^8 -> Sửa: 125-x^6   125-x^6   =5^3-(x^2)^3   =(5-x^2).[5^2+5.x^2+(x^2)^2]   =(5-x^2).(25+5x^2+x^4)

haianhtu97 · Answer

Giải đáp:      a)   36-12x+x^2   =6^2-2.6.x+x^2   =(6-x)^2   AD: a^2-2ab+b^2=(a-b)^2   b)   4x^2+12x+9   =(2x)^2+2.2x.3+3^2   =(2x+3)^2   AD: a^2+2ab+b^2=(a+b)^2   c)   -25x^6-y^8+10x^{3}y^{4}   =-(25x^6-10x^{3}y^{4}+y^8)   =-[(5x^3)^2-2.5x^{3}.y^{4}+(y^4)^2]   =-(5x^3-y^4)^2   AD: a^2-2ab+b^2=(a-b)^2   d)   1/4 x^2-5xy+25y^2   =(1/2 x)^2-2.(1)/(2)x.5y+(5y)^2   =(1/2 x-5y)^2   AD: a^2-2ab+b^2=(a-b)^2   e)   (x-5)^2-16   =(x-5)^2-4^2   =(x-5+4).(x-5-4)   =(x-1).(x-9)   AD: a^2-b^2=(a+b).(a-b)   f)   25-(3-x)^2   =5^2-(3-x)^2   =[5+(3-x)].[5-(3-x)]   =(5+3-x).(5-3+x)   =(8-x).(2+x)   AD: a^2-b^2=(a+b).(a-b)   g)   (7x-4)^2-(2x+1)^2   =[(7x-4)+(2x+1)].[(7x-4)-(2x+1)]   =(7x-4+2x+1).(7x-4-2x-1)   =(9x-3).(5x-5)   =3.(3x-1).5.(x-1)   =15.(3x-1).(x-1)   AD: a^2-b^2=(a+b).(a-b)   h)   8x^3+(1)/(27)   =(2x)^3+(1/3)^3   =(2x+1/3).[(2x)^2-2x. 1/3 +(1/3)^2]   =(2x+1/3).(4x^2-2/3 x+1/9)   AD: a^3+b^3=(a+b).(a^2-ab+b^2)   i)   M&igrave;nh sửa x^8->x^6 nh&eacute;.   125-x^6   =5^3-(x^2)^3   =(5-x^2).[5^2+5.x^2+(x^2)^2]   =(5-x^2).(25+5x^2+x^4)   AD: a^3-b^3=(a-b).(a^2+ab+b^2)