LEARNING OBJECTIVE: Discover how to use the cosine rule to find a missing angle
SUCCESS CRITERIA: You will be able to use the cosine rule to find the missing angle in a triangle
HINT: You have to use the re-arranged cosine rule to find the missing angle when you have all three sides of the triangle and NONE of the angles
STARTER: SOLVE THIS PROBLEM
The hour hand of a clock is 6.2 cm long, the minute hand is 4.5 cm long.
What is the distance between the ends of the hands at exactly 7 o'clock
LESSON: Use above example to revise using cosine rule to find a length then work through this lesson to look at using a re-arranged version of the cosine rule to find out an angle of a triangle when you know all three lengths but none of the angles.
Now have a go at Q2 page 488, then q6 onwards on page 488
In last 15 mins briefly look at formula for area of a triangle using this lesson Screen 4 onwards.
PLENARY: Checking answers, checking confidence of students on Sine Rule, Cosine Rule and Area of a triangle Rule