$\\$
Bài `2.`
`a,`
`A=53^2 + 94 .53 + 47^2`
`->A = 53^2 + 2 . 53 . 47 + 47^2`
`->A=(53 + 47)^2`
`->A=100^2`
`->A=100 00`
Vậy `A=100 00`
`b,`
`B = x^2 - y^2 - 2y -1`
`->B=x^2 - (y^2 + 2 . y .1 +1^2)`
`->B=x^2 - (y+1)^2`
`->B=(x-y-1)(x+y+1)`
Thay `x=97,y=2` vào `B` ta được :
`->B=(97 - 2-1)(97+2+1)`
`->B=94 . 100`
`->B=9400`
Vậy `B=9400` khi `x=97,y=2`
$\\$
Bài `3.`
`a,`
`(x+2)(x^2 - 2x+4)-x^2 (x+1)`
`=x^3 + 2^3- x^3 - x^2`
`= x^3 + 8 - x^3 - x^2`
`=8-x^2`
`b,`
`x^3 - 5x=0`
`<=>x (x^2-5)=0`
TH1 :
`x=0`
TH2 :
`x^2-5=0`
`<=> x^2=5`
`<=>x=±\sqrt{5}`
Vậy pt có tập nghiệm : `S={0; ±\sqrt{5} }`
`c,`
`8x^3 -1`
`= (2x)^3 - 1^3`
`= (2x-1)(4x^2 + 2x + 1)`
`(8x^3 - 1): (4x^2 +2x+1)`
`= (2x-1)(4x^2 +2x+1):(4x^2 +2x+1)`
`= (2x-1) [(4x^2 +2x+1):(4x^2 +2x+1)]`
`= 2x-1`
