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a= 10;b=15; c=20
Nếu muốn cách giải thì
http://olm.vn/hoi-dap/tim-kiem?q=Ai+c%C3%B2n+on+th%C3%AC+gi%C3%BAp+m%C3%ACnh+v%E1%BB%9Bi,+m%C3%ACnh+%C4%91ang+c%E1%BA%A7n+g%E1%BA%A5p:t%C3%ACm+a,b,c+bi%E1%BA%BFt+a=2b=3/2c+v%C3%A0+a^2++b^3-+%E2%88%9A((5^2)c)=a+b^3-5/3c&id=420882
a) ta có: \(\frac{a}{4}=\frac{b}{5};\frac{b}{5}=\frac{c}{8}\)
\(\Rightarrow\frac{a}{4}=\frac{b}{5}=\frac{c}{8}=\frac{5a}{20}=\frac{3b}{15}=\frac{3c}{24}\)
ADTCDTSBN
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bn tự áp dụng rùi tìm a;b;c nha
b) ta có: \(\frac{a+3}{5}=\frac{b-2}{3}=\frac{c-1}{7}=\frac{3a+9}{15}=\frac{5b-10}{15}=\frac{7c-7}{49}\)
ADTCDTSBN
có: \(\frac{3a+9}{15}=\frac{5b-10}{15}=\frac{7c-7}{49}=\frac{3a+9-5b+10+7c-7}{15-15+49}\)
\(=\frac{\left(3a-5b+7c\right)+\left(9+10-7\right)}{49}=\frac{86+12}{49}=\frac{98}{49}=2\)
=>...
c) ta cóL \(\frac{a}{7}=\frac{b}{6}\Rightarrow\frac{a}{35}=\frac{b}{30}\)
\(\frac{b}{5}=\frac{c}{8}\Rightarrow\frac{b}{30}=\frac{c}{48}\)
\(\Rightarrow\frac{a}{35}=\frac{b}{30}=\frac{c}{48}=\frac{2b}{60}\)
ADTCDTSBN
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các bài còn lại bn dựa vào mak lm nha!
a) A = \(9\frac{3}{8}-\left(2\frac{3}{5}+2\frac{3}{8}\right)=9\frac{3}{8}-2\frac{3}{5}-2\frac{3}{8}=\left(9\frac{3}{8}-2\frac{3}{8}\right)-2\frac{3}{5}=7-\frac{13}{5}=\frac{22}{5}\)
b) B = \(\left(15\frac{3}{5}+5\frac{3}{4}\right)-8\frac{3}{5}=15\frac{3}{5}+5\frac{3}{4}-8\frac{3}{5}=\left(15\frac{3}{5}-8\frac{3}{5}\right)+5\frac{3}{4}=7+\frac{23}{4}=\frac{51}{4}\)
c) C = \(17\frac{1}{4}-\left(2\frac{3}{7}+7\frac{1}{4}\right)=17\frac{1}{4}-2\frac{3}{7}-7\frac{1}{4}=\left(17\frac{1}{4}-7\frac{1}{4}\right)-2\frac{3}{7}=10-\frac{17}{7}=\frac{53}{7}\)
d) D = \(\left(11\frac{5}{17}+3\frac{5}{7}\right)-4\frac{5}{17}=11\frac{5}{17}+3\frac{5}{7}-4\frac{5}{17}=\left(11\frac{5}{17}-4\frac{5}{17}\right)+3\frac{5}{7}=7+\frac{26}{7}=\frac{75}{7}\)
a) \(3a=4b\Rightarrow\frac{a}{4}=\frac{b}{3}\)
Áp dụng dãy tỉ số bằng nhau , có : \(\frac{a}{4}=\frac{b}{3}=\frac{b-a}{3-4}=\frac{5}{-1}=-5\)
\(\Rightarrow a=-5\cdot4=-20\)
\(\Rightarrow b=-5\cdot3=-15\)
b) Từ \(2a=3b\Rightarrow\frac{a}{3}=\frac{b}{2}\Rightarrow\frac{a}{6}=\frac{b}{4}\) (1)
Tương tự : \(3b=4c\Rightarrow\frac{b}{4}=\frac{c}{3}\)(2) ;
Từ (1) và (2) ta có : \(\frac{a}{6}=\frac{b}{4}=\frac{c}{3}\)
Áp dụng t/c dãy tỉ số bằng nhau : \(\frac{a}{6}=\frac{b}{4}=\frac{c}{3}=\frac{a-b+c}{6-4+3}=\frac{35}{5}=7\)
\(\Rightarrow a=7\cdot6=42\)
\(\Rightarrow b=7\cdot4=28\)
\(\Rightarrow c=7\cdot3=21\)
c) \(\frac{a}{5}=\frac{b}{6}\Rightarrow\frac{a}{40}=\frac{b}{48}\) ; \(\frac{b}{8}=\frac{c}{7}\Rightarrow\frac{b}{48}=\frac{c}{42}\)
\(\Rightarrow\frac{a}{40}=\frac{b}{48}=\frac{c}{42}\)
Áp dụng t/c dãy tỉ số = nhau : \(\frac{a}{40}=\frac{b}{48}=\frac{c}{42}=\frac{a+b-c}{40+48-42}=\frac{69}{46}=\frac{3}{2}\)
\(\Rightarrow a=\frac{3}{2}.40=60\)
\(\Rightarrow b=\frac{3}{2}.48=72\)
\(c=\frac{3}{2}.42=63\)
\(\frac{a}{7}=\frac{b}{5}=\frac{c}{2}=\frac{2c}{4}=\frac{\left(a+b+c\right)}{7+5+2}=\frac{\left(a+b+c\right)}{14}=\frac{a-b-2c}{7-5-4}=\frac{6}{-2}=-3\)
\(\left(a+b+c\right)=-3\cdot14=-42\)