Răspuns: a = 7
Explicație pas cu pas:
a : b × b + a × b : b + a + a = 21 + a
a + a + 2 × a = 21 + a
4 × a - a = 21
3 × a = 21
a = 21 : 3
a = 7
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a : b × b = a × (1/ b ) × b = a
a × b : b = ( a × b ) × ( 1/b ) = a
