Cho tỉ lệ thức a/b=c/d.Chứng minh 2a2-3ab+5b2/2b2+3ab=2c2-3cd+5d2/2d2+3cd
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Cho tỉ lệ thức : \(\dfrac{a}{b}=\dfrac{c}{d}\) . Chứng minh : \(\dfrac{2a^2-3ab+5b^2}{2b^2+3ab}=\dfrac{2c^2-3cb+5b^2}{2b^2+3ab}=\dfrac{2c^2-3cd+5d^2}{2d^2+3cd}\) . Với điều kiện mẫu thức được xác định.
Cho tỉ lệ thức: a/b=c/d.Chứng minh
a)ab/cd=(a-b)^2/(cd)^2
b)(a+b/c+d)^2=a^2+b^2/c^2+d^2
c)7a^2+3ab/11a^2-8b^2=7c^2+3cd/11c^2-8d^2
Cho tỉ lệ thức a/b=c/d.chưng minh: \(\frac{2a^2-3ab+5b^2}{2b^2+3ab}=\frac{2c^2-3cd+5d^2}{2d^2+3cd}\)
Có bạn nào biết làm câu này không thì giúp mình nha mình đang cần gấp 9 giờ mình phải nộp cho cô rồi nếu được thì mình cảm ơn nhiều chỉ phải làm câu 3 bài 1 thôi nhé
O1=O2( vì 2 góc đối đỉnh)
O3 và O4 thì làm theo cách hai góc kề bù
Vd :O1+O3=180 độ (2 góc kề bù)
Suy ra :120 độ +O3=180 độ
Vậy từ đó tính ra đc O3 ,tương tự O4 cũng vậy
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Cho tỉ lệ thức : \(\frac{a}{b}=\frac{c}{d}\). Chứng minh : \(\frac{2a^2-3ab+5b^2}{2b^2+3ab}=\frac{2c^2-3cd+5d^2}{2d^2+3cd}\) . Với điều kiện mẫu thức xác định.
\(\frac{a}{b}=\frac{c}{d}\Rightarrow a=bk;c=dk\)
\(\frac{2a^2-3ab+5b^2}{2b^2+3ab}=\frac{2b^2k^2-3b^2k+5b^2}{2b^2+3b^2k}=\frac{b^2\left(2k^2-3k+5\right)}{b^2\left(2+3k\right)}=\frac{2k^2-3k+5}{3k+2}\)
\(\frac{2c^2-3cd+5d^2}{2d^2+3cd}=\frac{2d^2k^2-3d^2k+5d^2}{2d^2+3d^2k}=\frac{d^2\left(2k^2-3k+5\right)}{d^2\left(2+3k\right)}=\frac{2k^2-3k+5}{3k+2}\)
nên 2 phân số trên bằng nhau (đpcm)
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Đặt: \(\frac{a}{b}=\frac{c}{d}=k\Rightarrow\hept{\begin{cases}a=bk\\c=dk\end{cases}}\)
Ta có : \(\frac{2a^2-3ab+5b^2}{2b^2+3ab}\)
<=> \(\frac{2b^2k^2-3b^2k+5b^2}{2b^2+3b^2k}\)
<=> \(\frac{b^2\left(2k^2-3k+5\right)}{b^2\left(2+3k\right)}\)
<=> \(\frac{2k^2-3k+5}{2+3k}\left(1\right)\)
Ta có: \(\frac{2c^2-3cd+5d^2}{2d^2+3cd}\)
<=> \(\frac{2d^2k^2-3d^2k+5d^2}{2d^2+3d^2k}\)
<=> \(\frac{d^2\left(2k^2-3k+5\right)}{d^2\left(2+3k\right)}\)
<=> \(\frac{2k^2-3k+5}{2+3k}\left(2\right)\)
Từ 1 và 2 => đpcm
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Cho tỉ lệ thức: \(\frac{a}{b}=\frac{c}{d}\). Chứng minh: \(\frac{2a^2-3ab+5b^2}{2b^2+3ab}=\frac{2c^2-3cd+5d^2}{2d^2+3cd}\)
Bạn tham Khảo: https://hoc24.vn/hoi-dap/question/230602.html
Cho tỉ lệ thức: \(\dfrac{a}{b}=\dfrac{c}{d}\). Chứng minh:
\(\dfrac{2a^2-3ab+5b^2}{2b^2+3ab}=\dfrac{2c^2-3cd+5d^2}{2d^2+3cd}\)
Đặt: \(\dfrac{a}{b}=\dfrac{c}{d}=k\\ \Rightarrow a=bk;c=dk\)
Ta có:
\(\dfrac{2a^2-3ab+5b^2}{2b^2+3ab}=\dfrac{2\left(bk\right)^2-2bkb+5b^2}{2b^2+3bkb}=\dfrac{2b^2k^2-2b^2k+5b^2}{2b^2+3b^2k}=\dfrac{b^2\left(2k^2-3k+5\right)}{b^2\left(2+3k\right)}=\dfrac{2k^2-3k+5}{2+3k}\left(1\right)\)
\(\dfrac{2c^2-3cd+5d^2}{2d^2+3cd}=\dfrac{2\left(dk\right)^2-3dkd+5d^2}{2d^2+3dkd}=\dfrac{2d^2k^2-3d^2k+5d^2}{2d^2+3d^2k}=\dfrac{d^2\left(2k^2-3k+5\right)}{d^2\left(2+3k\right)}=\dfrac{2k^2-3k+5}{2+3k}\left(2\right)\)
Từ (1) và (2) suy ra:
\(\dfrac{2a^2-3ab+5b^2}{2b^2+3ab}=\dfrac{2c^2-3cd+5d^2}{2d^2+3cd}\)
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Giải:
Đặt \(\dfrac{a}{b}=\dfrac{c}{d}=k\Rightarrow\left\{{}\begin{matrix}a=bk\\c=dk\end{matrix}\right.\)
Ta có: \(\dfrac{2a^2-3ab+5b^2}{2b^2+3ab}=\dfrac{2b^2k^2-3b^2k+5d^2}{2b^2+3b^2k}\)
\(=\dfrac{b^2k\left(2k-3k+5\right)}{b^2\left(2+3k\right)}=\dfrac{k\left(2k-3+5\right)}{2+3k}\) (1)
\(\dfrac{2c^2-3cd+5d^2}{2d^2+3cd}=\dfrac{2d^2k^2-3d^2k+5d^2}{2d^2+3d^2k}\)
\(=\dfrac{d^2k\left(2k-3+5\right)}{d^2\left(2+3k\right)}=\dfrac{k\left(2k-3+5\right)}{2+3k}\) (2)
Từ (1), (2) \(\Rightarrow\dfrac{2a^2-3ab+5b^2}{2b^2+3ab}=\dfrac{2c^2-3cd+5d^2}{2d^2+3cd}\left(đpcm\right)\)
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18 tháng 8 2021 lúc 7:51
có ai biết làm bài này không giúp mình với mình đang cần rất rất là gấp mong các bạn giúp cho , xin cảm ơnII. Choose the best answer1.I come from Canada. Where .................you..................from?a. do.............come b. did ...... come c. are ..........coming d, have .....come2. The telephones…………..by Alexander Graham BellA. is invented B. is inventing C. Invented D. was invented3. The swimming pool .............. at 9 o’clock...
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có ai biết làm bài này không giúp mình với mình đang cần rất rất là gấp mong các bạn giúp cho , xin cảm ơn
II. Choose the best answer
1.I come from Canada. Where .................you..................from?
a. do.............come b. did ...... come c. are ..........coming d, have .....come
2. The telephones…………..by Alexander Graham Bell
A. is invented B. is inventing C. Invented D. was invented
3. The swimming pool .............. at 9 o’clock and ............ at 18.30 everyday.
a. opens............. closes b. opens ...... closed c. opened...... closed d. opened......... closes
4. Three swimmers, Paul, Ed, and Jim, ................ now in competition for medals.
a. is b. has been c. had been d. are
5. Listen ! I .............. somebody knocking at the front door.
a. am hearing b. heard c. have heard d. hear
6.. ………………………………………..yet?
A. Have the letters been typed B. Have been the letters typed
C. Have the letters typed D. Had the letters typed
7. At 5 o’clock yesterday evening, I ……………my clothes.
a. am ironing b. have ironed c. ironed d. was ironing.
8. I ………………..along the street when I suddenly heard footsteps behind me.
a. was walking b. am walking c. walk d. walked.
9. She ………….German for two years.
a. has learnt b. is learning c. learn d. learns.
10. When I last………..Jane, she ………..to find a job.
a. see/was trying b. saw/was trying c. have seen/tried d. saw/tried.
12. French is a…………language to learn than English is.
A. difficult B. more difficult C. most difficult D. more and more difficult
13. The more polluted air we breathe,…….we get.
A. the more weaker B. the more weak
C. the weaker D. weaker more
14. The more we study, the……we are.
A. more good B. better C. better than D. good
15. The more I tried my best to help her, ……….she became.
A. less lazy B. the lazier C. the more lazy D. lazier
16. The weather becomes………………
A. colder with colder B. colder and colder
C. colder and more colder D. more and more cold
17. The more he slept,…………….irritable he became.
A. the most B. the vey more C. much more D. the more
18. ………..he worked, the more he earned.
A. The more hard B. The hard C. The harder D. The hardest
19. ………I get to know Jim, the more I like him.
A. For more B. More C. The more D. The most
20. The competition makes the price of goods……….
A. most cheap and cheap B. cheaper and cheaper
C. more cheap and more cheap D. cheaper and more cheaper
III. Rewrite:
1) Although Tom was a poor student, he studied very well.
=> In spite of ………………………………………………………
2) Mary could not go to school because she was sick.
Because of ………………………………………………………………..
3) Although the weather was bad, she went to school on time.
=> Despite ……………………………………………………………..
4) My mother told me to go to school although my stomachache was sick.
=> In spite of ………………………………………………………………..
5) Because there was a big storm, I stayed at home.
=> Because of ……………………………………………………..
6) Tom was admitted to the university although his grades were bad.
Despite …………………………………………………………………………
7) Although she has a physical handicap, she has become a successful woman.
=> Despite ……………………………………………………………………….
8) In spite of his good salary, Tom gave up his job.
=> Although………………………………………………………..
II.
1. a
2. d
3. a
4. d
5. d
6. a
7. d
8. a
9. a
10. b
12. b
13. c
14. b
15. b
16. b
17. d
18. c
19. c
20. b
III.
1. In spite of being a poor student, Tom studied very well.
2. Because of her sickness, Mary could not go to school.
3. Despite the bad weather, she went to school on time.
4. In spite of my sick stomachache, my mother told me to go to school.
5. Because of the big storm, I stayed at home.
6. Despite his bad grades, Tom was admitted to the university.
7. Despite her physical handicap, she has become a successful woman.
8. Although his salary was good, Tom gave up his job.
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16 tháng 10 2015 lúc 21:53
Cho tỉ lệ thức : \(\frac{a}{b}=\frac{c}{d}\)
Chứng minh : \(\frac{2a^2-3ab+5b^2}{2b^2+3ab}=\frac{2c^2-3cd+5d^2}{2d^2+3cd}\) . Với điều kiện mẫu thức xác định.
