Consider the following worksheet:
(a) In a spreadsheet, every formula starts with a/an ................. sign.
(b) Write the formula to calculate the amount for Glue stick. (Amount is calculated as Price $\times$ Quantity)
$PQ$ is a chord of length $4\ \text{cm}$ of a circle of radius $2.5\ \text{cm}$. The tangents at $P$ and $Q$ intersect at a point $T$. Find the length of $TP$.