A convex set is a set where, for any two points in the set, the line segment connecting them lies entirely within the set. In this case, the triangle is a convex set because any line segment connecting two points in the triangle lies entirely within the triangle.

A convex function is a function where, for any two points in the domain, the line segment connecting the corresponding points on the graph of the function lies entirely above or on the graph of the function. In this case, $f(x) = x^2$ is a convex function because the graph of the function is a parabola that opens upwards.

A convex optimization problem is an optimization problem where the objective function is convex and the constraints are convex sets. In this case, the objective function $f(x) = x^2 + y^2$ is convex and the constraint $x + y \le 1$ defines a convex set, so the problem is a convex optimization problem.

The Interior Point Method is a widely used algorithm for solving convex optimization problems. It works by iteratively moving towards the optimal solution while staying within the feasible region defined by the constraints.

Convex optimization has a wide range of applications, including portfolio optimization, supply chain management, and machine learning. In portfolio optimization, convex optimization is used to find the optimal allocation of assets in a portfolio to maximize returns while minimizing risk. In supply chain management, convex optimization is used to optimize the flow of goods and services through a supply chain to minimize costs and maximize efficiency. In machine learning, convex optimization is used to train machine learning models by minimizing a loss function.