Đáp án+Giải thích các bước giải:
`a)`Ta có:
`(1+2+3+4)^2=10^2=100`
`1^3+ 2^3+ 3^3+ 4^3=1+8+27+64=9+27+64=33+64=100`
Vậy `(1+2+3+4)^2=1^3+ 2^3+ 3^3+ 4^3`
__________________________________________________________________________
`b)`Ta có:`19^4`
`16.18.20.22`
`=(18.20).(22.16)`
`=(19-1)(19+1)(19+3)(19-3)`
`=(19^2-1)(19^2-9)`
`=19^2. 19^2+(-1).(-9)`
`=19^4+9`
Vì `19^4+9>19^4`
`=>16.18.20.22>19^4`
Vậy `16.18.20.22>19^4`
__________________________________________________________________________
`c)`Ta có:`345^2`
`342.348`
`=(345-3)(345+3)`
`=345.345+(-3).3`
`=345^2 -9`
Vì `345^2 -9<345^2`
`=>345^2>342.348`
Vậy `345^2>342.348`
__________________________________________________________________________
`d)` Ta có:`874^2`
`870.878`
`=(874-4)(874+4)`
`=874.874+(-4).4`
`=874^2-16`
Vì `874^2-16<874^2`
`=>874^2>870.878`
Vậy `874^2>870.878`
