I'm doing some marking for a year 8 (12 to 13-year-old) scholarship paper and I saw this symbol that looks like the Sputnik probe and I have no idea what it is, does anyone know?
[Math] Maths symbol that looks like Sputnik
notation
Related Solutions
It is the interior product (Wikipedia page, MathWorld page). It's defined on page 334-336 of Lee's book:
It's the characteristic function (or indicator function) of the set in the subscript.
$$\mathbb 1_A(x) = \begin{cases} 1\,, & x\in A \\ 0\,, & x\notin A\end{cases}.$$
Best Answer
I think it is a typesetting problem with the parentheses.
My best guess at the intended question would be:
$$\left( 2-\frac 12 \right) \left( 2-\frac 23 \right) \left( 2-\frac 34 \right) \left( 2-\frac 45 \right)$$
This seems reasonable given the level of the other questions.