Question

1) Thuc hien phep tinh (nhanh neu co the):

a) 21.(-35)-3.(-25).7

b) 77-11.(30+7)

c) 85.(35-27)-35.(85-27)

d) (-25).68+(-34).(-250)

e) 125.(-61).(-2³).(-1)²ⁿ⁺¹/ n thuoc N

f) 1-2+3-4+...+49-50+51

g)1-2-3+4+5-6-7+...+97-98-99+100

h) 2¹⁰⁰-2⁹⁹-2⁹⁸-...-2²-2-1

Làm đc câu nào thì làm nha

Answer 1

a) 21.(-35)-3.(-25).7=21.(-35)-(21.(-25)=21(-35+25)=21.(-10)=-210

b)77-11(30+7)=77-11.7+11.30=77-77-330=-330

c)85(35-27)-35(85-27)=85.35-85.27-35.85+35.27=(85.35-35.85)+(35.27-85.27)=35.27-85.27=27(35-85)=27.(-50)=-1350

d)(-25).68+(-34).(-250)=-25.68+34.2.125=-25.68+68.125=68(125-25)=68.100=6800

e)125.(-61).(-2^3).(-1)^2n+1=125.(-61).(-8).(-1)=(-8.125).61=-1000.61=-61000

h) đặt S=2¹⁰⁰-2⁹⁹-2⁹⁸-...-2²-2-1=2^100-(2^99+2^98+2^97+...+2+1)=2^100-A

ta có: A=2^99+2^98+2^97+...+2+1

2A=2^100+2^99+2^98+...+2^2+2

=>2A-A=(2^100+2^99+2^98+...+2^2+2)-(2^99+2^98+2^98+...+2+1)

=>A=2^100-1

=>S=2^100-(2^100-1)=2^100-2^100+1=1

A=2^100

Answer 2

a là bằng -210

ý b bằng -330

ý c bằng -1350

ý d bằng 6800

ý f bằng 225

tớ làm được 5 ý , tich nha bạn

Answer 3

a, 21.(-35)-3.(-25).7

=21.(-35)-(3.7).(-25)

=21.(-35)-21.(-25)

=21.[(-35)-(-25)]

=21.(-10)

=-210