tính nhanh:
-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1+20
đúng ( t i c k ) cho dễ lắm
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\(\left\{\left(1-\dfrac{1}{2}\right).\left(1-\dfrac{1}{3}\right).\left(1-\dfrac{1}{4}\right).\left(1-\dfrac{1}{5}\right)\right\}\)
=\(\dfrac{1}{2}.\dfrac{2}{3}.\dfrac{3}{4}.\dfrac{4}{5}\)
\(=\dfrac{1}{5}\)
chúc bạn học tốt
1-1/2. 1-1/3. 1-1/4. 1-1/5
= 0/2. 0/3. 0/4. 0/5
= 0. 0. 0. 0
= 0
1.\(\left(\dfrac{1}{2}+1\right)\cdot\left(\dfrac{1}{3}+1\right)\cdot\left(\dfrac{1}{4}+1\right)..\left(\dfrac{1}{999}+1\right)\)
\(=\left(\dfrac{1}{2}+\dfrac{2}{2}\right)\cdot\left(\dfrac{1}{3}+\dfrac{3}{3}\right)\cdot...\left(\dfrac{1}{999}+\dfrac{999}{999}\right)\)
\(=\dfrac{3}{2}\cdot\dfrac{4}{3}\cdot...\cdot\dfrac{1000}{999}\)\(=\dfrac{3\cdot4\cdot5\cdot...\cdot1000}{2\cdot3\cdot4\cdot...\cdot999}\)
\(=\dfrac{1000}{2}=500\).
2.
\(\left(\dfrac{1}{2}-1\right)\cdot\left(\dfrac{1}{3}-1\right)\cdot...\cdot\left(\dfrac{1}{1000}-1\right)\)
\(=\left(\dfrac{1}{2}-\dfrac{2}{2}\right)\cdot\left(\dfrac{1}{3}-\dfrac{3}{3}\right)...\left(\dfrac{1}{1000}-\dfrac{1000}{1000}\right)\)
Thôi mai mk làm tiếp nha
1/2+1/4+1/8+1/16+1/32+1/64
=2x(1/2+1/4+1/8+1/16+1/321/64)
=1+1/2+1/4+1/8+1/16+1/32
=1+1/2+1/4+1/8+1/16+1/32-1/2-1/4-1/8-1/16-1/32-1/64
=1-1/64
=63/64
\(\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}\)
\(=\frac{32}{64}+\frac{16}{64}+\frac{8}{64}+\frac{4}{64}+\frac{1}{64}+\frac{1}{64}\)
\(=\frac{62}{64}=\frac{31}{32}\)
1/1x2 + 1/2x3 + 1/3x4 + 1/4x5 + 1/5x6
Đặt A = 1/1x2 + 1/2x3 + 1/3x4 + 1/4x5 + 1/5x6
A = 1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6
A = 1/1 - 1/6
A = 5/6
Vậy A = 5/6
P = \(\left(1-\frac{1}{2}\right)\left(1-\frac{1}{3}\right)...\left(1-\frac{1}{99}\right)\)
= \(\frac{1}{2}.\frac{2}{3}.....\frac{98}{99}\)
= \(\frac{1}{99}\)
\(B=\frac{1}{2}x\frac{2}{3}x\frac{3}{4}x\frac{4}{5}x...x\frac{2002}{2003}x\frac{2003}{2004}\)
\(B=\frac{1x2x3x4x...x2002x2003}{2x3x4x5x...x2003x2004}\)
Rút gọn các thừa số ở tử và mẫu ta được:
\(B=\frac{1}{2004}\)
Đ/S:\(\frac{1}{2004}\)
Ta có:
\(\left(1-\frac{1}{2}\right).\left(1-\frac{1}{3}\right)....\left(1-\frac{1}{2003}\right).\left(1-\frac{1}{2004}\right)\)
\(=\frac{1}{2}.\frac{2}{3}....\frac{2002}{2003}.\frac{2003}{2004}\)
\(=\frac{1.2....2002.2003}{2.3....2003.2004}\)
Đơn giản hết sẽ là:
\(=\frac{1}{2004}\)
-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1+20
=(-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1)+20
=-20+20
=0
nhớ ck cho tớ đó
= -20+20
= 0