Answer with Step-by-step explanation:
Since we have given that
a + b = c
and a|c
i.e. a divides c.
We need to prove that a|b.
⇒ a = mb for some integer m
Since a|c,
So, mathematically, it is expressed as
c= ka
Now, we put the above value in a + b = c.
So, it becomes,

a=mb, here, m = k-1
Hence, proved.
11:
1. 123°
2. 57°
3. 95
4. 85°
12.
1. 130°
2. 54°
3. 130°
4. 126°