The SUMSQ function syntax has the following arguments: Number1, number2, ... Number1 is required, subsequent numbers are optional. 1 to 255 arguments for which you want the sum of the squares. You can also use a single array or a reference to an array instead of arguments separated by commas.
THEY/THEIR (SINGULAR). Using the plural pronoun to refer to a single person of unspecified gender is an old and honorable pattern in English, not a newfangled bit of degeneracy or a politically correct plot to avoid sexism (though it often serves the latter purpose).
Some nouns have the same form in the singular and the plural. Some nouns have a plural form but take a singular verb. Some nouns have a fixed plural form and take a plural verb. They are not used in the singular, or they have a different meaning in the singular. Nouns like this include: trousers, jeans, glasses, savings, thanks, steps, stairs, customs, congratulations, tropics, wages, spectacles, outskirts, goods, wits.