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a fost răspuns

5 la puterea x-1 +5 la puterea x-2 + 5 la puterea x-3 =775 , 3*7 la puterea x +3*7 la puterea x+1 +7 la puterea x=2 ajutorrrrrrrrrrr

Răspuns :

Nseara
5^(x-1)+5^(x-2)+5^(x-3)=775
5^2*5^(x-3)+5^1*5^(x-3)+5^(x-3)=775
25*5^(x-3)+5*5^(x-3)+5^(x-3)=775
31*5^(x-3)=775
5^(x-3)=25
5^(x-3)=5^2
x-3=2
x=5.

3*7^x+3*7^(x+1)+7^x=2
3*7^x+3*7^1*7^x+7^x=2
3*7^x+21*7^x+7^x=2
25*7^x=2
7^x=2/25
x=log in baza 7 din 2/25.

PS: am impresia ca a doua ecuatie e scrisa gresit. Verifica eventual. Sarbatori frumoase!
5^x·5⁻¹+5^x·5⁻²+5^x·5⁻³=775
5^x(1/5+1/5²+1/5³)=775
5^x(1/5+1/25+1/125)=775
5^x(25+5+1)/125=775
5^x·31/125=775
5^x·31=775·125
5^x=(775·125)/31
5^x=25·125
5^x=5⁵
x=5

3·7^x+3·7^x·7+7^x=2
7^x(3+3·7+1)=2
7^x(3+21+1)=2
7^x·25=2
7^x=2/25
ceva nu ai scris corect mai verifica-l

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