Sine and Cosine Rule revision PRESS F 5

Sine and Cosine Rule revision PRESS F 5

Sine and Cosine Rule revision PRESS F 5 Then spacebar to step through slideshow. Attempt the Q’s – you won’t get anywhere simply viewing someone else doing the maths

Sine rule If there are two angles involved in the question it’s a Sine rule question. Use this version of the rule to find angles: Sin A = Sin B = Sin C a b c e. g. 1 A b C a 620 7 m B Use this version of the rule to find sides: a = b = c. Sin A Sin B Sin C c 23 m Sin A = Sin B = Sin C a b c Sin = Sin B = Sin 62 7 b 23 Sin = Sin 62 x 7 23 Sin = 0. 2687 = 15. 60 e. g. 2 C b 520 a 8 m B a = b = c. Sin A Sin B Sin C 8 = b = ? . Sin 9 Sin B Sin 52 ? = 8 x Sin 52 Sin 9 ? = 40. 3 m 90 ? c A

If there is only one angle involved (and all 3 sides) it’s a Cosine rule question. Cosine rule Use this version of the rule to find sides: a 2 = b 2 + c 2 – 2 bc Cos A Use this version of the rule to find angles: Cos A = b 2 + c 2 – a 2 2 bc C e. g. 1 2. 3 m c ? a 32 cm b B 670 A 45 cm c Always label the one angle involved - A B a 2 = b 2 + c 2 – 2 bc Cos A a 2 = 322 + 452 – 2 x 32 x 45 x Cos 67 a 2 = 3049 – 1125. 3 a = 43. 86 cm A e. g. 2 2. 1 m b 3. 4 m a Cos A = b 2 + c 2 – a 2 2 bc Cos = 2. 12 + 2. 32 – 3. 42 2 x 2. 1 x 2. 3 Cos = - 1. 86 9. 66 = 101. 10 C