mn ơi e vít nhầm là tính rồi rút gọn mn sửa lại là rút gọn rùi tính

a: =2/5+3/5=1

b: =1/3+5/6=2/6+5/6=7/6

c: =7/8+5/8=12/8=3/2

d: =2/3+2/10

=20/30+6/30

=26/30=13/15

e: =1/2+1/3

=3/6+2/6

=5/6

f: =2/7+1/6

=12/42+7/42

=19/42

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\(\dfrac{5}{15}=\dfrac{5:5}{15:5}=\dfrac{1}{3}\\ \dfrac{28}{56}=\dfrac{28:28}{56:28}=\dfrac{1}{2}\\ \dfrac{48}{96}=\dfrac{48:48}{96:48}=\dfrac{1}{2}\\ \dfrac{15}{120}=\dfrac{15:15}{120:15}=\dfrac{1}{8}\\ \dfrac{60}{80}=\dfrac{60:20}{80:20}=\dfrac{3}{4}\)

còn phân số 24 / 30 bn ILoveMath ơi

giúp mik với ạ!!!

Câu 1: C

Câu 2: A

Đặt phân số trên là A

\(A=\frac{25^{28}+25^{24}+...+25^4+25^0}{\left(25^{28}+25^{24}+...+25^4+25^0\right)+\left(25^{30}+25^{26}+...+25^6+25^2\right)}\)

\(\frac{1}{A}=\frac{\left(25^{28}+25^{24}+...+25^4+25^0\right)+\left(25^{30}+25^{26}+...+25^6+25^2\right)}{25^{28}+25^{24}+...+25^4+25^0}\)

\(\frac{1}{A}=1+\frac{25^{30}+25^{26}+...+25^6+25^2}{25^{28}+25^{24}+...+25^4+25^0}\)

Đặt \(B=\frac{25^{30}+25^{26}+...+25^6+25^2}{25^{28}+25^{24}+...+25^4+25^0}\)

\(\frac{B}{25^2}=\frac{25^{30}+25^{26}+...+25^6+25^2}{25^{30}+25^{26}+...+25^6+25^2}=1\Rightarrow B=25^2\)

=> \(\frac{1}{A}=1+B=1+25^2\Rightarrow A=\frac{1}{1+25^2}\)
 

rễ như trễ bàn tay mà cũng hỏi

Mình cần gấp. Mong các bạn giúp đỡ

Đặt \(A=\frac{5^{28}+5^{24}+.........+5^4+1}{5^{30}+5^{28}+5^{26}+.....+5^2+1}=\frac{B}{C}\)

Xét tử \(B=5^{28}+5^{24}+........+5^4+1\)

\(\Rightarrow5^4.B=5^{32}+5^{28}+........+5^8+5^4\)

\(\Rightarrow625.B=5^{32}+5^{28}+........+5^8+5^4\)

\(\Rightarrow625.B-B=624.B=5^{32}-1\)

\(\Rightarrow B=\frac{5^{32}-1}{624}\)

Xét mẫu \(C=5^{30}+5^{28}+5^{26}+........+5^2+1\)

\(\Rightarrow5^2.C=5^{32}+5^{30}+5^{28}+.........+5^4+5^2\)

\(\Rightarrow25.C=5^{32}+5^{30}+5^{28}+........+5^4+5^2\)

\(\Rightarrow25.C-C=24.C=5^{32}-1\)

\(\Rightarrow C=\frac{5^{32}-1}{24}\)

\(\Rightarrow A=\frac{B}{C}=\frac{5^{32}-1}{624}:\frac{5^{32}-1}{24}=\frac{5^{32}-1}{624}.\frac{24}{5^{32}-1}=\frac{24}{624}=\frac{1}{26}\)

Đặt \(B=5^{28}+5^{24}+...+5^4+1\Rightarrow5^4B=5^{32}+5^{28}+...+5^8+5^4\)

\(\Rightarrow\left(5^4-1\right)B=5^{32}-1\Rightarrow B=\frac{5^{32}-1}{5^4-1}\)

Đặt \(C=5^{30}+5^{28}+...+5^2+1\Rightarrow5^2C=5^{32}+5^{30}+...+5^4+5^2\)

\(\Rightarrow\left(5^2-1\right)C=5^{32}-1\Rightarrow C=\frac{5^{32}-1}{5^2-1}\)

Khi đó \(A=\frac{B}{C}=\frac{\frac{5^{32}-1}{5^4-1}}{\frac{5^{32}-1}{5^2-1}}=\frac{5^2-1}{5^4-1}=\frac{1}{26}\)

                     Vậy................

a) \(\frac{2}{5}+\frac{9}{15}=\frac{2}{5}+\frac{3}{5}=\frac{5}{5}=1\)

b) \(\frac{15}{45}+\frac{25}{30}=\frac{1}{3}+\frac{5}{6}=\frac{2}{6}+\frac{5}{6}=\frac{7}{6}\)

c) \(\frac{28}{32}+\frac{45}{72}=\frac{7}{8}+\frac{5}{8}=\frac{12}{8}=\frac{3}{2}\)

d) \(\frac{8}{28}+\frac{5}{30}=\frac{2}{7}+\frac{1}{6}=\frac{12}{42}+\frac{7}{42}=\frac{19}{42}\)

a) \(\frac{2}{5}+\frac{9}{15}\)=\(\frac{2}{5}+\frac{3}{5}=\frac{2+3}{5}=1\)

b)\(\frac{15}{45}+\frac{25}{30}=\frac{1}{3}+\frac{5}{6}=\frac{2}{6}+\frac{5}{6}=\frac{2+5}{6}=\frac{7}{6}\)

c)\(\frac{28}{32}+\frac{45}{72}=\frac{7}{8}+\frac{5}{8}=\frac{7+5}{8}=\frac{12}{8}=\frac{3}{2}\)

d)\(\frac{8}{28}+\frac{5}{30}=\frac{2}{7}+\frac{1}{6}=\frac{12}{42}+\frac{7}{42}=\frac{12+7}{42}=\frac{19}{42}\)

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