CHAPTER 17. TRIGONOMETRY 17.5
SOLUTIONApplying the cosine rule:a^2 = b^2 + c^2 − 2 bccosAˆ∴ cosAˆ =
b^2 + c^2 − a^2
2 bc=82 + 5^2 − 72
2. 8. 5
= 0, 5
∴ Aˆ = 60◦
Exercise 17 - 12
- Solve the following triangles i.e. find all unknown sidesand angles
(a)�ABC in whichAˆ = 70◦; b = 4 and c = 9(b)�XY Z in whichYˆ = 112◦; x = 2 and y = 3(c)�RST in which RS = 2; ST = 3 and RT = 5(d)�KLM in which KL = 5; LM = 10 and KM = 7(e)�JHK in whichHˆ = 130◦; JH = 13 and HK = 8(f)�DEF in which d = 4; e = 5 and f = 7- Find the length of thethird side of the�XY Z where:
(a)Xˆ = 71, 4 ◦; y = 3, 42 km and z = 4, 03 km(b) ; x = 103, 2 cm;Yˆ = 20, 8 ◦and z = 44, 59 cm- Determine the largest angle in:
(a)�JHK in which JH = 6; HK = 4 and JK = 3(b)�P QR where p = 50; q = 70 and r = 60More practice video solutions or help at http://www.everythingmaths.co.za