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a+b=13 , a-c=5 , calculati 9×a + 4×b -5×c

Răspuns :

a+b = 13
a-c = 5
adunam cele 2 ecuatii
2a+b-c = 18
9×a+4×b-5c =
= 4(2a+b-c)+(a-c )
= 4×18+5 
= 72+5 
= 77