Which option is NOT a valid type of trendline application?

A quadratic trendline is indeed a valid type of trendline application, which is a specific case of polynomial trendlines. Generally, trendlines are used in data analysis to visually represent trends in data points and help with predictions based on observed trends.

Linear trendlines indicate a straight-line relationship, polynomial trendlines can fit multiple curves depending on their degree, and exponential trendlines model scenarios where growth accelerates over time. Each of these trendline types serves a purpose in identifying the nature of data relationships.

In this context, since all the mentioned types are valid applications, the answer suggesting that quadratic is not a valid trendline is incorrect. The proper choice among options would actually affirm that each mentioned type fulfills a specific analytical role in data representation.