Tính nhanh :80^2-79^2+78^2-77^2+….+2^2-1 17/08/2021 Bởi Julia Tính nhanh :80^2-79^2+78^2-77^2+….+2^2-1
`80²-79²+78²-77²+….+2²-1` `=(80²-79²)+(78²-77²)+…+(2²-1²)` `=(80-79)(80+79)+(78-77)(78+77)+…+(2-1)(2+1)` `=80+79+78+77+…+2+1` `=3240` Xin hay nhất ! Bình luận
80²-79²+78²-77²+….+2²-1 =(80²-79²)+(78²-77²)+…+(2²-1²) =(80-79)(80+79)+(78-77)(78+77)+…+(2-1)(2+1) =80+79+78+77+…+2+1 =80(80+1):2=3240 Bình luận
`80²-79²+78²-77²+….+2²-1`
`=(80²-79²)+(78²-77²)+…+(2²-1²)`
`=(80-79)(80+79)+(78-77)(78+77)+…+(2-1)(2+1)`
`=80+79+78+77+…+2+1`
`=3240`
Xin hay nhất !
80²-79²+78²-77²+….+2²-1
=(80²-79²)+(78²-77²)+…+(2²-1²)
=(80-79)(80+79)+(78-77)(78+77)+…+(2-1)(2+1)
=80+79+78+77+…+2+1
=80(80+1):2=3240