Giải thích các bước giải:
a)
`A=(-3-5).(-3+5)`
`=(-8).2`
`=-16`.
`B= -3/7 . 5/9+ 4/9 . (-3)/7+2019 3/7`
`= -3/7.(5/9+ 4/9)+2019 3/7`
`=-3/7.1+2019 3/7`
`=-3/7 + 2019 3/7`
`=2019`.
b)
`P=(1-1/4).(1-1/9).` `...` `.(1-1/2500)`
`=>P=3/4. 8/9.` `...` `. 2499/2500`
`=>P=1.3/2.2. 2.4/3.3.` `...` `. 49.51/50.50`
`=>P=(1.2...49)/(2.3...50). (3.4...51)/(2.3...50)`
`=>P=1/50. 51/2`
`=>P=51/100>50/100=1/2` hay `P>1/2`.
Vậy `P>1/2`.