Answer:
#See details below
Step-by-step explanation:
#An isosceles triangle has two equal angles:[tex]\angle FEC=2\angleCAB\\\\\angle FEC=\angle DCB \ \ \ \ \ \#Co-alternate \ angles\\\\\angle ACB= 180 -\angle DCB\ \ \ \ \ \#angles \ on \ a \ straight \ line\\\\\angle CAB=180-\angle ACB=\angle CBA[/tex]
#An isosceles triangle has two equal sides;
Using sine rule:
[tex]\frac{a}{sin \ A}=\frac{b}{sin \ B}\\\\\frac{ac}{sin B}=\frac{cb}{sin A} \ \ \ \ \ \ \ \ \ \ \ \ #\angle CAB=\angle CBA\\\\\therefore ac=cb[/tex]
Now, given that ABC has two equal sides and two equal triangle it is an isosceles triangle.
