Question

Tìm a,b, c biết : 2a = 3b; 5b = 7c; 3a+5c-7b = 30 

Answer 1

\(2a=3b;5b=7c\Rightarrow\frac{a}{3}=\frac{b}{2};\frac{b}{7}=\frac{c}{5}\Rightarrow\frac{a}{21}=\frac{b}{14};\frac{b}{14}=\frac{c}{10}\)

\(\Rightarrow\frac{a}{21}=\frac{b}{14}=\frac{c}{10}\)

áp dụng tính chất của dãy tỉ số băng nhau bằng nhau ta có:

\(\frac{a}{21}=\frac{b}{14}=\frac{c}{10}=\frac{3a+5c-7b}{3.21+5.10-7.14}=\frac{30}{15}=2\)

suy ra: \(\frac{a}{21}=2\Rightarrow a=2.21=42\)

\(\frac{b}{14}=2\Rightarrow b=2.14=28\)

\(\frac{c}{10}=2\Rightarrow c=2.10=20\)

Answer 2

a=42

b=28

c=20

Answer 3

A=42

B=28

C=20

Answer 4

a=42                                                                                                                                                                                           b=28                                                                                                                                                                                           c=20

Answer 5

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Chuc ban hoc dot

Answer 6

tự làm đi

Answer 7

Cho tam giác ABC cường ở a trên toàn AC lấy điểm Dsao cho AD=AC Chứng minh tam giác ABC= tam giác ABD