Using named tuples in select statements

Is there a nicer way to select a named tuple in C# 7 using a var target variable? I must be doing something wrong in example 1, or misunderstanding something completely. I seem to have to explicitly set the target type in order to do this.

//1. Fails to compile with "incorrect number of type parameters" issue.
var tuples = source.Select<(int A, int B)>(x => (x.A, x.B));

//2. Compiles
IEnumerable<(int A, int B)> tuples = toCheck.Select(x => (x.A, x.B));

//3. Compiles
var tuples = new HashSet<(int A, int B)>(source.Select(x => (x.A, x.B)));