Câu hỏi của Cao Hà

Question

21) 125x3 -122) 4x4 - 9x223) 64x2 - 25y424) 4( a + b )2 - 9( a - b )225) 8( x + 1 )3 - 27( x - 1 )3

Lightning Farron · Accepted Answer

21) 125x3 -1=125x3-13=(5x-1)(25x2+5x+1)22) 4x4 - 9x2=x2(4x2-9)=x2(4x2-32)=x2(2x-3)(2x+3)23) 64x2 - 25y4=(8x)2-(5y2)2=(8x-5y2)(8x+5y2)24) 4( a + b )2 - 9( a - b )2=22(a+b)2-32(a-b)2=[2(a+b)]2-[3(a-b)]2=[2(a+b)-3(a-b)][2(a+b)+3(a-b)]=(2a+2b-3a+3b)(2a+2b+3a-3b)=(5a-b)(5b-a)25) 8( x + 1 )3 - 27( x - 1 )3=23(x+1)3-33(x-1)3=[2(x+1)]3-[3(x-1)]3={[2(x+1)]-[3(x-1)}{[2(x+1)]2+[2(x+1)]*[3(x-1)]+[3(x-1)]2}={2x+2-3x+3}{4x2+8x+4+6x2-6+9x2-18x+9}=(5-x)(19x2-10x+7) Câu trả lời: 21) 125x3 -1=125x3-13=(5x-1)(25x2+5x+1)22) 4x4 - 9x2=x2(4x2-9)=x2(4x2-32)=x2(2x-3)(2x+3)23) 64x2 - 25y4=(8x)2-(5y2)2=(8x-5y2)(8x+5y2)24) 4( a + b )2 - 9( a - b )2=22(a+b)2-32(a-b)2=[2(a+b)]2-[3(a-b)]2=[2(a+b)-3(a-b)][2(a+b)+3(a-b)]=(2a+2b-3a+3b)(2a+2b+3a-3b)=(5a-b)(5b-a)25) 8( x + 1 )3 - 27( x - 1 )3=23(x+1)3-33(x-1)3=[2(x+1)]3-[3(x-1)]3={[2(x+1)]-[3(x-1)}{[2(x+1)]2+[2(x+1)]*[3(x-1)]+[3(x-1)]2}={2x+2-3x+3}{4x2+8x+4+6x2-6+9x2-18x+9}=(5-x)(19x2-10x+7)

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