Non-native speakers often struggle when they have to speak about powers. For example, the correct expression used for is ten to the power of three, although it is common to instead use the shorter form ten to the three. Similarly, is x to the (power of) seven. The exponents 2 and 3 (can you think of other examples?) have special names: is x squared, is x cubed. A confusing yet common mistake is to say ten to three (which refers to the time of day 2:50) instead of ten to the three. If the exponent is negative, for example , the correct expression is 10 to the (power of) minus three, but not 10 to the (power of) negative three. Finally, the correct form for is either exponential function of x or, much shorter, e to the (power of) x.