4.如图，$△ ABC ≌ △ DCB$，若$∠ A=80°$，$∠ DBC=40°$，则$∠ DCA$的度数为
20°
。
答案：4.20°
5.如图，$△ EFG ≌ △ NMH$，$∠ F$与$∠ M$是对应角.
(1)求证:$FH=GM$；
(2)若$FH=1.1\ \mathrm{cm}$，$HM=3.3\ \mathrm{cm}$，求$HG$的长度.
答案：5.(1)证明:$\because △ EFG≌△ NMH$,$∠ F$与$∠ M$是对应角,
$\therefore FG=MH$,$\therefore FG-HG=MH-HG$,即$FH=GM$.
(2)解:$\because △ EFG≌△ NMH$,$\therefore FG=HM=3.3\ \mathrm{cm}$,
$\therefore HG=FG-FH=3.3-1.1=2.2(\mathrm{cm})$.
