a: =-10/13-3/13+5/17+12/17-11/20=-11/20

b: =9/4-10/12+11/12=10/12=5/6

c: =(-7+8)/15=1/15

d: =-9/15+10/15=1/15

e: \(=\dfrac{-10}{36}+\dfrac{20}{35}-\dfrac{11}{36}=\dfrac{-42}{36}=-\dfrac{7}{6}\)

f: \(=\dfrac{-7}{21}+\dfrac{8}{24}=\dfrac{1}{3}-\dfrac{1}{3}=0\)

a)2 + 5 + 11 + ... + 47+ 95
Tính chất : 5 = 2.2 + 1
11 = 5.2 + 1
Vậy các số của dãy là: 2 + 5 + 7 + 11 + 23 + 47 + 95
= (2 + 5 + 7) + (5 + 95) + (23 + 47)
= 14 + 100 + 70
= 184

\(n_{C_2H_2}=\dfrac{2,24}{22,4}=0,1\left(mol\right)\)

PT: \(C_2H_2+2Br_2\rightarrow C_2H_2Br_4\)

Theo PT: \(n_{Br_2}=2n_{C_2H_2}=0,2\left(mol\right)\Rightarrow C_{M_{Br_2}}=\dfrac{0,2}{0,2}=1\left(M\right)\)

→ Đáp án: C

câu 1 là A sai

Câu 1: A

Câu 2: C

B

Các bạn ơi, giúp tớ câu này, tớ đang cần gấp

B

\(A=3^{n+3}+3^{n-1}+2^{n+2}+2^{n+1}\)

\(=3^n\cdot\left(27+\dfrac{1}{3}\right)+2^n\left(4+2\right)\)

\(=3^{n-1}\cdot2\cdot41+2^n\cdot6⋮6\)

nó cứ sai sai sao ý

\(\frac{75.5^4+175.5^4}{20.25.125-625.75}=\frac{\left(75+175\right).5^4}{4.5.25.5^3-5^4.75}\)

\(=\frac{250.5^4}{100.5^4-5^4.75}=\frac{250.5^4}{\left(100-75\right).5^4}\)

\(=\frac{250}{25}=10\)

1 .......... good that I have watched it 3 times

2 .......... it rained heavily, we didn't get wet as we got home

4 I admire the girl who didn't hesitate to save the kids from the crazy bus

5 ......... am excited about seeing you this weekend