I’ve just been marking your Chapter 2 assessments – and overall they were pretty good (an average mark of over 79%), however I’m using this blog to help some of you pick up some extra marks.
Two relatively uncommon, but easily corrected mistakes:
- Not rounding to 3sf when asked.
- Using incorrect sine and cosine rule formulae (definitely no excuses on an open book assessment!).
I’m also going to go over a couple of the less well answered questions – namely Q7b and Q8.
On Q7b it said that is cos(A) = 3/4, find the exact value of sin(A). The mark scheme gave two possible ways to answer this question – one was using the trigonometric identity below which I’m not sure if you have covered with Mrs P yet.
Alternatively, you could recreate the triangle which would give you cos(A) = 3/4 – see this solution by Mr McBride (sorry, my scanner isn’t working – this is a photo of what he wrote on one of your assessments during P6):
For Q8, you needed to use the ambiguous case of the sine rule (see this blog post if you need a reminder).
I’m going to give you a few hints, then if you could complete the question and resubmit it to me I can increase your assessment grade.
- There are two possible triangles that could be created – find one of the missing angles and then do 180 – that angle to find the other one.
- Decide if there’s any other information that you need before substituting into the area rule (clue – there is, don’t just substitute these angles in straightaway).
- Find the areas
- Find the difference between the areas.