Algebra
代數
Algebra uses letters to stand for numbers we do not know yet. In this lesson you will learn about variables, expressions, simplifying, and substitution.
代數用字母代表我們還不知道的數。在這一課，你會學習變數、代數式、簡化和代入。
1 · What is algebra?
甚麼是代數？
Algebra uses letters to stand for numbers we do not know yet. For example, x + 3 = 7 means "some number plus 3 equals 7". Algebra helps us find unknown values.
代數用字母代表我們還不知道的數。例如 x + 3 = 7，是指「某個數加 3 等於 7」。代數幫助我們找出未知的值。
2 · Variables and expressions
變數與代數式
A variable is a letter that stands for a number, like x or y. An expression is a combination of numbers and variables, like 3x + 2. The number in front of a variable is the coefficient.
變數是代表數字的字母，例如 x 或 y。代數式是數字和變數的組合，例如 3x + 2。變數前面的數是係數。
In 3x + 2, the coefficient is 3, the variable is x, and 2 is the constant.
在 3x + 2 中，係數是 3，變數是 x，2 是常數。
3 · Simplifying expressions
簡化代數式
You can simplify an expression by combining like terms. Like terms have the same variable. 2x + 3x = 5x. But 2x + 3y cannot be combined because x and y are different.
你可以合併同類項來簡化代數式。同類項有相同的變數。2x + 3x = 5x。但 2x + 3y 不能合併，因為 x 和 y 不同。
4 · Substitution
代入
Substitution means replacing a variable with a number. If x = 4, then 3x + 2 = 3 × 4 + 2 = 12 + 2 = 14.
代入是指用數字取代變數。如果 x = 4，那麼 3x + 2 = 3 × 4 + 2 = 12 + 2 = 14。
5 · Quick check
小測驗