🇹🇭 อ่านบทนี้เป็นภาษาไทย — รูปเรขาคณิตสองมิติและสามมิติ (ชั้นมัธยมศึกษาปีที่ 1)
Chapter 8
Angles, Shapes and Symmetry
Angles, Shapes and Symmetry
The angle facts that every later geometry proof is built from, the properties that name a triangle or a quadrilateral, and the two kinds of symmetry.
- หลักสูตรแกนกลาง / สสวท.
- การวัดและเรขาคณิต (Geometry and Measure)ตรงกับ ม.1 บทที่ 5 รูปเรขาคณิตสองมิติและสามมิติ และบทที่ 2 การสร้าง
- Common Core (US)
- 7.G, 8.G
- Cambridge
- Lower Secondary Stage 7 — Geometry and Measure: geometrical reasoning, shapes and measurements
8.1 Angle facts
- The facts, and what they are called
- Angles on a straight line add to
- Angles around a point add to
- Vertically opposite angles are equal
- Angles in a triangle add to
- Angles in a quadrilateral add to
- Naming angles by size
- acute — less than
- right — exactly
- obtuse — between and
- reflex — more than
ข้อควรระวัง
Never measure an angle off the page to answer a question. Diagrams in exams are not drawn to scale, and it is stated so precisely because a measured answer would otherwise sometimes be right, which is worse than always being wrong.
ตัวอย่าง
Two angles on a straight line are and . Find .
วิธีทำ
- 1.Angles on a straight line add to
- 2.
- 3.
ตอบ
เคล็ดลับ
Always write the reason next to the step, in words: "angles on a straight line". At this stage it earns marks; two years later it is the difference between an answer and a proof.
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