# On the pronunciation of the second derivative

I have been looking at Lancelot Hogben's Mathematics for the Million (first published in 1936).

In the chapter on calculus he says that the second derivative $\displaystyle \frac{d^2y}{dx^2}$ is

pronounced dee-two-wy-by-dee-eks-two.

The final "two" surprised me as I was taught to say "squared" and I have never heard it pronounced differently.

Assuming that it's not a typo and that Prof Hogben wasn't mistaken, did people really say "two" in those days and does anyone say "two" these days?

I suppose that for higher derivatives just saying the number rather than the power it represents may be easier.

• Well, maybe he meant that $\dfrac{d^2y}{dx^2}$ is $\dfrac{d^2y}{dx}$ too. ;-) Commented Jul 18, 2013 at 10:27
• i've heard a lot of people saying it this way
– Aang
Commented Jul 18, 2013 at 10:31
• I usually say "the second derivative of $y$ with respect to $x$" ...
– Neal
Commented Jul 18, 2013 at 11:03
• I say "squared" in the place of the first "two" too: "dee-squared-wy-by-dee-eks-squared". If we can find someone who says "dee-squared-wy-by-dee-eks-two", all $2^2$ possibilities will have been covered. Commented Jul 18, 2013 at 11:53

According to this post there are several ways to pronounce $\frac {d^2y}{dx^2}$, including: