Use sine law to explain why the 2 equal sides of an isoceles triangle must be opposite the two equal angles

Answer 1

if sides a and b are equal, then

a/sinA = b/sinB
means that

a/sinA = a/sinB
so sinA = sinB

Now, A and B need not be equal if their sines are equal, but in that case A = 180°-B and your triangle is just a flat line.