19. A man sold a cow for $80, and gained c dollars. What did the cow cost?
20. If the sum of two numbers is 60, how may the numbers be represented?
4. ILLUS. 1. 4 * 5 * a * b * c, 7 x 6, x x y.
ILLUS. 2. abc, xy, amx.
ILLUS. 3. x * x = xx = x2.
x * x * x = xxx = x3.
These two are read “x second power,” or “x square,” and “x third power,”
or “x cube,” and are called powers of x.
A power is a product of like factors.
The 2 and the 3 are called the exponents of the power.
An exponent is a number expressed at the right and a little above another
number to show how many times it is taken as a factor.
Multiplication is expressed (1) by signs, i.e. the dot and the cross;
(2) by writing the factors successively; (3) by exponent.
The last two are the more common methods.
When use the exponent? When write the factors successively?
1. Express the double of x.
2. Express the product of x; y, and z.
3. How many cents in x dollars?
4. Write a times b times c.
5. What will a quarts of cherries cost at d cents a quart?
6. If a stage coach, goes b miles an hour, how far will it go in m hours?
7. In a cornfield there are x rows, and a hills in a row. How many hills in
8. Write the cube of x.
9. Express in a di®erent way a x a x a x a x a x a x a x a x a.
10. Express the product of a factors each equal to d.
11. Write the second power of a added to three times the cube of m.