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Lacramioaratancau
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daca 2a-3b=15 si a-b=4, calculeaza 5a-7b? ​

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Răspuns:

[tex]2a-3b = 15\\\\a-b = 4 \Rightarrow a = b+4\\\\2b+8-3b=15 \Rightarrow-b = 15-8 \Rightarrow-b = 7 \Rightarrow \boxed{b = -7}\\\\a = -7+4 \Rightarrow \boxed{a=-3}\\\\5a-7b = 5*(-3)-7*(-7) = -15 +49 \Rightarrow \boxed{5a-7b=34}[/tex]