`#Sad`
`68)`
`x^3+3x^2+3x+1`
`= x^3+3. x^2. 1+3. x. 1^2+1^3`
`= (x+1)^3`
`69)`
`x^3+6x^2+12x+8`
`= x^3+3. x^2. 2+3. x. 2^2+2^3`
`= (x+2)^3`
`70)`
`x^3+9x^2+27x+27`
`= x^3+3. x^2. 3+3. x. 3^2+3^3`
`= (x+3)^3`
`71)`
`x^3+12x^2+48x+64`
`= x^3+3. x^2. 4+3. x. 4^2+4^3`
`= (x+4)^3`
`72)`
`x^3+15x^2+75x+125`
`= x^3+3. x^2. 5+3. x. 5^2+5^3`
`= (x+5)^3`
`\text{→Áp dụng:}` `A^3+3A^2B+3AB^2+B^3`
`73)`
`m^3-3m^2+3m-1`
`= m^3-3. m^2. 1+3. m. 1^2-1^3`
`= (m-1)^3`
`74)`
`m^3-6m^2+12m-8`
`= m^3-3. m^2. 2+3. m. 2^2-2^3`
`= (m-2)^3`
`75)`
`27-27m+9m^2-m^3`
`= 3^3-3. 3^2.m+3. 3. m^2-m^3`
`= (3-m)^3`
`76)`
`64-48m+12m^2-m^3`
`= 4^3-3. 4^2. m+3. 4. m^2-m^3`
`= (4-m)^3`
`77)`
`125-75m+15m^2-m^3`
`= 5^3-3. 5^2. m+3. 5. m^2-m^3`
`= (5-m)^3`
`\text{→Áp dụng:}` `A^3-3A^2B+3AB^2-B^3`
`78)`
`8a^3+12a^2+6a+1`
`= (2a)^3+3. (2a)^2. 1+3. 2a. 1^2+1^3`
`= (2a+1)^3`
`79)`
`8a^3-12a^2+6a-1`
`= (2a)^3-3. (2a)^2. 1+3. 2a. 1^2-1^3`
`= (2a-1)^3`
`80)`
`27a^3-27a^2+9a-1`
`= (3a)^3-3. (3a)^2. 1+3. 3a. 1^2-1^3`
`= (3a-1)^3`
`81)`
`27a^3+27a^2+9a+1`
`= (3a)^3+3. (3a)^2. 1+3. 3a. 1^2+1^3`
`= (3a+1)^3`
