Afla nr.necunoscut 78-(a+21)=46

Răspuns :

78-(a+21)=46
(a+21)=78-46
a+21=32
a=32-21
a=11

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PROBA:78-(11+21)=78-32=46
78-(a+21)=46
78-a-21=46
-a=46-78+21
-a=-32+21
-a=-11 |×(-1)
a=11