Răspuns: [tex]\boxed{\boxed{\bf \dfrac{7}{8}}}[/tex]
Explicație pas cu pas:
Salutare!
[tex]\bf \dfrac{7^{21} }{7^{20}+7^{21}} =[/tex]
[tex]\bf \dfrac{7^{21} }{7^{20}\cdot(7^{20-20}+7^{21-20})} =[/tex]
[tex]\bf \dfrac{7^{21} }{7^{20}\cdot(7^{0}+7^{1})} =[/tex]
[tex]\bf \dfrac{7^{21} }{7^{20}\cdot(1+7)} =[/tex]
[tex]\bf \dfrac{7^{21} }{7^{20}\cdot 8} =[/tex]
[tex]\bf \dfrac{7^{20}\cdot 7^{1} }{7^{20}\cdot 8} =\boxed{\boxed{\bf \dfrac{7}{8}}}[/tex]
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