Can anybody help me with these two questions:

1. Given a triangle with the 'base' at the bottom, single angle at the top. The base line is extended to the right. The exterior angle is 90 + (x/2). The top angle is x. How do I prove that it is isosceles?

2. Explain why the (n+1)th term of a triangular sequence is given by

1/2(n+1)(n+2) given that the nth term is 1/2n(n+1)