7. ABCD — ромб, ∠ABC = 55°. Найти: ∠BAD.

Соседние углы ромба в сумме дают $180^\backslash (\backslash circ\backslash )$:

$\backslash (\backslash angle\backslash )\; BAD=180^\backslash (\backslash circ\backslash )-\backslash (\backslash angle\backslash )\; ABC=180^\backslash (\backslash circ\backslash )-55^\backslash (\backslash circ\backslash )=125^\backslash (\backslash circ\backslash ).$

Ответ: $\backslash (\backslash angle\backslash )\; BAD=125^\backslash (\backslash circ\backslash )$.