程功节费开略有术 -北齐颜之推 s ppose a candy bar costs 45 cents. then 45 x 2 is the cost of 2 candy bars, 45 x 3 is the cost of 3 candy bars, and so on. generally, the cost of any n mber of candy bars is 45 cents times the n mber of bars. we can represent this sit ation with an algebraic expression. 假如一只冰棍花费45分.那么45 x 2 就是两只冰棍的花费,45 x 3 就是三只冰棍的花费,等等.一般来说,若干冰棍的花费就是45分乘冰棍数.我们可以用代数式表达这种情况. 45分 乘 冰棍数 45 x n the letter n stands for an nknown n mber, in this case, candy bars. the nknown n is called a variable beca se its val e varies. an algebraic expression contains at least one variable and at least one mathematical operation, as shown in the examples below. 字母n代表未知数,此例中,就是代表若干冰棍.未知数n称为变量,因为它的值可变.代数式至少包括一个变量,至少一个数学运算,如下列诸例所示. a n merical expression contains only n mbers and mathematical operations. for example, is a n merical expression. 一个算数式只包括数和数学运算.例如:是一个算数式. in an expression involving m ltiplication, the q antities being m ltiplied are called factors, and the res lt is the prod ct. 涉及乘法的式子里,相乘的量称为乘数,该结果是积. to write a m ltiplication expression s ch as 4 x a, a raised dot or parentheses can be sed. a fraction bar can be sed to represent division. 要写乘式,如 4 x a,就使用一个抬高的点或括号.分数的横线用来表示除法. the res lt of a division expression is called a q otient. 除式的结果称为商.