## Girls’ Angle Bulletin, Volume 8, Number 5

Volume 8, Number 5 of the Bulletin kicks off with an interview of Ivana Alexandrova. Ivana is an Assistant Professor of Mathematics at the State University of New York, Albany.  Among other things, she maintains a webpage of weekly problems for high school students. Check it out!

The topic of induction came up quite a few times this spring at the Girls’ Angle club, so next comes an article on this widely used proof technique.

This issue’s Learn by Doing features irrational numbers and culminates in a series of problems that let you reconstruct a proof of the irrationality of $\pi$ due to Charles Hermite.

Anna tackles one of Prof. Alexandrova’s weekly problems for high school students in Anna’s Math Journal, finding 3 different ways to solve the problem, which is to compute $\cos 72^\circ \cos 36^\circ$. Can you find your own solution?

Next comes our 4th installment on the derivative where we find the derivatives of the basic trigonometric functions. The way we deduce the derivative of sine is similar in spirit to the way we showed that the area under one hump of a sine curve is exactly 2.

Since this is our June issue, we include the 2015 Summer Fun problem sets. This batch contains problems pertaining to telescoping series (by Fan Wei), induction, the symmetric group (by Noah Fechtor-Pradines), and derivatives.

We hope you enjoy it!

Finally, a reminder: when you subscribe to the Girls’ Angle Bulletin, you’re not just getting a subscription to a magazine. You are also gaining access to the Girls’ Angle mentors.  We urge all subscribers and members to write us with your math questions or anything else in the Bulletin or having to do with mathematics in general. We will respond. We want you to get active and do mathematics. Parts of the Bulletin are written to induce you to wonder and respond with more questions. Don’t let those questions fade away and become forgotten. Send them to us!

We continue to encourage people to subscribe to our print version, so we have removed some content from the electronic version.  Subscriptions are a great way to support Girls’ Angle while getting something concrete back in return.  We hope you subscribe!