Question

a+3b=7
2b-5c=9
Atunci calc.
a) a+5b-5c=
b) 3a+7b+5c=

Answer 1

[tex]a +3b=7 =\ \textgreater \ a=7-3b \\ 2b-5c =9=\ \textgreater \ -5c=9-2b |*(-1)=\ \textgreater \ 5c=-9+2b =\ \textgreater \ c= \frac{2b-9}{5} \\[/tex]

$a+5b-5c=7-3b+5b-5* \frac{2b-9}{5}= \\ =7-3b+5b-2b+9=16-5b+5b= \\ =16$

[tex]3a+7b+5c=3(7-3b)+7b+5* \frac{2b-9}{5} = \\ =21-9b+7b+2b-9=12-9b+9b=12[/tex]

Answer 2

a+3b=7
2b-5c=9
 se aduna cele doua relatii 
a+3b+2b-5c= 7+9
a+5b-5c=16
b) a+3b=7
2b-5c=9
inmultim prima relatie cu 3
3a+9b= 21
2b -5c=9
scadem cele doua relatii
3a+9b-2b+5c= 21-9
3a+7b +5c= 12