Cosine Rule

The cosine rule connects the three sides of a triangle with one angle: $a^{2}=b^{2}+c^{2}-2bc\cos A$. It is used when we know two sides and the included angle, or all three sides.

When the angle is $90^\circ$ it reduces to Pythagoras' theorem.

You meet Cosine Rule in the Solution of Triangles chapter of SPM Additional Mathematics. Knowing the term precisely matters in the exam: questions often hinge on reading a keyword correctly, and because SPM marking is analytic, using the right definition in your working helps secure method marks.

Our teachers make sure a student can not only recite what Cosine Rule means but use it fluently in a full solution.

Because the SPM Add Math paper is bilingual (BM/EN), it helps to know this term in each language: Cosine Rule (EN) · Petua Kosinus (BM) · 余弦定理 (中文)

Other key terms from the Solution of Triangles chapter you may want to check:

• Sine Rule
• Ambiguous Case
• Area of a Triangle
• Heron's Formula
• Included Angle