sine rule 正弦定理.docVIP

LESSON PLAN FORMAT Course: Bilingual math Grade Level: grade 2 Teacher:Bela Date: Title: sine rule Content: Trigonometry PRE-LESSON PLANNING Learning Objectives Learn to deduct the theorem of sine rule Understand the meaning of sine rule Be able to use sine rule to solve question Design the Assessment Exercise page 198 Design Assessment Rubric (if Needed) TEACHING THE LESSON Vocabulary: Materials: IGCSE MATHEMATICS BOOK procedure New knowledge Triangles that aren’t Right Angled To find unknown sides and angles in non-right angled triangles we can use one or both of 2 rules: the sine rule The cosine rule The next few slides prove the sine rule. The cosine rule is on the next presentation. The Sine Rule ABC is a scalene triangle a, b and c are the sides opposite angles A, B and C Draw the perpendicular, h, from C to BA. In ⊿CAN, Sin A = In ⊿BCN, SinB= So, b sin A=h and asin B=h The triangle ABC . . . . . . can be turned so that BC is the base. We would then get So, We now have and So, The sine rule can be used in a triangle when we know One side and its opposite angle, plus One more side or angle e.g. Suppose we know p, q and angle Q in triangle PQR Tip: We need one complete “pair” to use the sine rule. The angle or side that we can find is the one that completes another pair. Solution: Use Solution: As the unknown is a side, we “flip” the sine rule over. The unknown side is then at the “top”. Application Problems Angle TDA =180 – 35 = 145? gAngle DTA =180 – 170 = 10?n SUMMARY The sine rule can be used in a triangle when we know One side and its opposite angle, plus One more side or angle We write the sine rule so that the unknown angle or side is on the left of the equation If 2 sides and 1 angle are known we use: If 1 side and 2 angles are known we use: Exercises Check for Student Understanding by: Guided Practice Check for student understanding by: Some exercise Closing Act