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Ajutati-ma va rog!!!
Calculati 3a + 4b - 5c , daca stim ca a,b,c sunt invers proportionale cu nr. [tex] \frac{1}{3} [/tex] ; [tex] \frac{1}{4} [/tex] ; [tex] \frac{1}{5} [/tex] 


Răspuns :

a,b,c invers prop cu 1/3.1/5.1/5
[tex] \frac{a}{ \frac{1}{1/3} } = \frac{b}{ \frac{1}{1/4} } = \frac{c}{ \frac{1}{1/5} } =k[/tex]
[tex] \frac{a}{3} = \frac{b}{4}= \frac{c}{5} =k[/tex]
a=3k
b=4k
c=5k
3*3k+4*4k-5*5k=9k+16k-25k=0