Expressions, Equations and Formulae

Letters standing for numbers — how to build an expression, simplify it, substitute into it, and solve the equations that result.

หลักสูตรแกนกลาง / สสวท.: จำนวนและพีชคณิต (Number and Algebra)ตรงกับ ม.1 บทที่ 6 สมการเชิงเส้นตัวแปรเดียว
Common Core (US): 6.EE, 7.EE
Cambridge: Lower Secondary Stage 7 — Algebra: expressions, equations and formulae

6.1 Algebraic notation

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The conventions, and why they exist
- $3 \times n$ is written $3 n$ — the multiplication sign is dropped because it looks too much like the letter $x$
- $n \div 4$ is written $\frac{n}{4}$
- $n \times n$ is written $n^{2}$
- The number goes before the letter: $3 n$ , never $n 3$

นิยาม

Expression, equation, formula

An expression has no equals sign ( $3 n + 2$ ). An equation states two things are equal and can be solved ( $3 n + 2 = 14$ ). A formula is a rule connecting quantities ( $A = l w$ ).

ข้อควรระวัง

"Simplify" and "solve" are different instructions. You simplify an expression and get another expression; you solve an equation and get a value. Answering the wrong one loses the marks even when the algebra is right.

English	ภาษาไทย
variable	ตัวแปร
coefficient	สัมประสิทธิ์
term	พจน์
expression	นิพจน์
equation	สมการ
substitute	แทนค่า

Key terms

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