Răspuns:
Explicație pas cu pas:
a)
[tex] \frac{3}{7} = \frac{a}{28} \Longrightarrow a = \frac{3 \times 28}{7} = \frac{84}{7} = \blue{\bf{} 12} \\ [/tex]
b)
[tex] \frac{a}{2} = \frac{7}{3,5} \Longrightarrow a = \frac{7 \times 2}{3,5} = \frac{14}{3,5} =\blue{ \bf{} 4 }\\ [/tex]
c)
[tex] \frac{4}{a} = \frac{a}{9} \Longrightarrow a {}^{2} = 4 \times 9 = 36 \Longrightarrow a = \sqrt{36} = \blue{\bf{} 6} \\ [/tex]
d)
[tex] \frac{0,6}{2a} = \frac{0,9}{21} \\ [/tex]
[tex]2 \times a \times 0,9 = 0,6 \times 21[/tex]
[tex]1,8\times a = 12,6 \Longrightarrow a = \frac{12,6}{1,8} = \blue{\bf{} 7} \\ [/tex]
