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`a, 27x^3 + 27x^2 + 9x +1`
`= (3x)^3 + 3*9x^2*1 + 3*3x + 1`
`= (3x + 1)^3`
Thay `x=13` ta có :
`(3*13+1)^3`
`= 40^3`
`= 64000`
`b, x^3 - 15x^2 + 75x - 125`
`= x^3 - 3*x^2*5+ 3*x*25 - 5^3`
`= (x-5)^3`
Thay `x=35` ta có :
`(35-5)^3`
`= 30^3`
`= 27000`
`c, x^3 + 12x^2 + 48x + 65`
Thay `x=6` ta có :
`6^3 + 12*6^2 + 48*6 + 65`
`= 216 + 432 + 288 + 65`
`= 1001`