câu 8, 9, 10 hộ nhé
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ND
20
OM
12 tháng 7 2017
số cần tìm là
1 + 2 + 3 + 4 + 5 + 6+ 7 + 8 + 9 + 10 = 55
đáp số 55
OA
27 tháng 7 2017
1.
=3/5x(3/7+4/7)+2/5x(13/9-4/9)
=3/5x1+2/5x1
=3/5+2/5
=1
2.Xx(3/4+4/5)=7/10
Xx31/20=7/10
X =7/10:31/20
X =14/31
TH
28 tháng 7 2017
\(\frac{3}{5}\cdot\frac{3}{7}+\frac{3}{5}\cdot\frac{4}{7}+\frac{2}{5}\cdot\frac{13}{9}-\frac{2}{5}\cdot\frac{4}{9}\)
\(=\frac{3}{5}\cdot\left(\frac{3}{7}+\frac{4}{7}\right)+\frac{2}{5}\cdot\left(\frac{13}{9}-\frac{4}{9}\right)\)
\(=\frac{3}{5}\cdot1+\frac{2}{5}\cdot1\)\(=\frac{3}{5}+\frac{2}{5}=1\)
_________________________________________
\(\frac{3}{4}\cdot x+\frac{4}{5}\cdot x=\frac{7}{10}\)
\(\left(\frac{3}{4}+\frac{4}{5}\right)\cdot x=\frac{7}{10}\)
\(\frac{31}{20}\cdot x=\frac{7}{10}\)
\(x=\frac{7}{10}:\frac{31}{20}\)
\(x=\frac{14}{31}\)
ND
0
28 tháng 9 2021
1, What time does your father het up and have breakfast?
2, Ha's house is in the country abd it's small
3, How many cities are there in your country?
4, How did your family get to PQ island?
5, Jane goes to school at eight o' clock every morning
6, Does Hung live in the country or in the city?
7, Did you take part in the sports festival?
8, Hoa invited Minh to her birthday party
9, My family went to my cousin's birthday party last night
10, What did you do on Mid-Autumn festival?
11,My classmate went on a trip to the zoo by bus
12, We enjoyed the food and drinks at the party
LV
1
15 tháng 11 2021
a) 1 - 3 + 5 - 7 + 9 - 11
= (1 - 3) + (5 - 7) + (9 - 11)
= (-2) + (-2) + (-2)
= -6
b) -14 - 16 - 18 - ... - 92
= - (14 + 16 + 18 + .... + 92)
Áp dụng công thức tính dãy số ta có :
14 + 16 + 18 + .... + 92 = 2120
= -2120
c) 15 + 18 + 21 + .... + 63 + 66 + 70
= (15 + 18 + 21 + ..... + 66) + 70
Áp dụng công thức tính dãy số ta có :
15 + 18 + ..... + 66 = 729
= 729 + 70
= 8799
d) 2 - 3 + 4 - 5 + 6 - 7 + 8 - 9 + 10
= (2 - 3) + (4 - 5) + (6 - 7) + (8 - 9) + 10
= (-1) + (-1) + (-1) + (-1) + 10
= 6
Câu 9.
\(x^3-19x-30=0\)
\(\Leftrightarrow x^3+2x^2-2x^2-4x-15x-30=0\)
\(\Leftrightarrow\left(x+2\right)\left(x^2-2x-15\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(x^2-5x+3x-15\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(x-5\right)\left(x+3\right)=0\)
\(\Leftrightarrow\hept{\begin{cases}x_1=-2\\x_2=5\\x_3=-3\end{cases}}\)
\(B=x_1^2+x_2^2+x_3^2=38\)
Câu 10.
\(2a>b>0\Rightarrow2\frac{a}{b}>1\Leftrightarrow t>\frac{1}{2}\)(\(t=\frac{a}{b}\))
\(4a^2+b^2=5ab\)
\(\Leftrightarrow4\left(\frac{a}{b}\right)^2+1-5\frac{a}{b}=0\)
\(\Leftrightarrow4t^2-4t-t+1=0\)
\(\Leftrightarrow\left(4t-1\right)\left(t-1\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}t=\frac{1}{4}\left(l\right)\\t=1\left(tm\right)\end{cases}}\)
\(A=\frac{ab}{4a^2-b^2}=\frac{t}{4t^2-1}=\frac{1}{4-1}=\frac{1}{3}\)