Comments on: Mr Brewin’s Year 9 – Sine and Cosine Rules http://www.shsmaths.com/2010/03/mr-brewins-year-9-sine-and-cosine-rules/ Tue, 07 Feb 2012 21:11:26 +0000 hourly 1 http://wordpress.org/?v=3.0.4 By: Mr Brewin http://www.shsmaths.com/2010/03/mr-brewins-year-9-sine-and-cosine-rules/comment-page-1/#comment-6634 Mr Brewin Sun, 14 Mar 2010 21:54:56 +0000 http://www.shsmaths.com/?p=1479#comment-6634 OK, you have to rearrange the cosine rule to do that. If A is opposite the 12cm side: A = Cos-1[ (6^2 +8^2 - 12^2)/(2 x 8 x 6) ] Make sense? OK, you have to rearrange the cosine rule to do that. If A is opposite the 12cm side:

A = Cos-1[ (6^2 +8^2 - 12^2)/(2 x 8 x 6) ]

Make sense?

]]> By: Sophie Hart http://www.shsmaths.com/2010/03/mr-brewins-year-9-sine-and-cosine-rules/comment-page-1/#comment-6633 Sophie Hart Sun, 14 Mar 2010 21:19:49 +0000 http://www.shsmaths.com/?p=1479#comment-6633 It tells you the measurements for all of the sides (6cm, 12cm and 8cm), but it doesn't tell you any of the angles. You have to work out the angle opposite the 12cm side. I have no idea even where to begin! :( It tells you the measurements for all of the sides (6cm, 12cm and 8cm), but it doesn’t tell you any of the angles. You have to work out the angle opposite the 12cm side. I have no idea even where to begin! :(

]]> By: Mr Brewin http://www.shsmaths.com/2010/03/mr-brewins-year-9-sine-and-cosine-rules/comment-page-1/#comment-6632 Mr Brewin Sun, 14 Mar 2010 20:38:02 +0000 http://www.shsmaths.com/?p=1479#comment-6632 Sorry Sophie - not got the question sheet here with me, but what you've written for 22.2 1e sounds pretty good. If you could describe the question for 22.3 1 I'll have a go, but sounds like you've put in a good stint, so just come see me tomorrow! Sorry Sophie – not got the question sheet here with me, but what you’ve written for 22.2 1e sounds pretty good. If you could describe the question for 22.3 1 I’ll have a go, but sounds like you’ve put in a good stint, so just come see me tomorrow!

]]> By: Sophie Hart http://www.shsmaths.com/2010/03/mr-brewins-year-9-sine-and-cosine-rules/comment-page-1/#comment-6631 Sophie Hart Sun, 14 Mar 2010 19:50:17 +0000 http://www.shsmaths.com/?p=1479#comment-6631 i am completely stuck on ex22.3 1. e), how do you work it out? and also, for ex22.2 1. e), does 8 ÷ 10/sin61 = sin y ? i am completely stuck on ex22.3 1. e), how do you work it out? and also, for ex22.2 1. e), does 8 ÷ 10/sin61 = sin y ?

]]> By: Mr Brewin http://www.shsmaths.com/2010/03/mr-brewins-year-9-sine-and-cosine-rules/comment-page-1/#comment-6630 Mr Brewin Wed, 10 Mar 2010 22:03:07 +0000 http://www.shsmaths.com/?p=1479#comment-6630 Come and see me tomorrow Aalia if you can. Come and see me tomorrow Aalia if you can.

]]> By: Mrs Tibble http://www.shsmaths.com/2010/03/mr-brewins-year-9-sine-and-cosine-rules/comment-page-1/#comment-6629 Mrs Tibble Wed, 10 Mar 2010 21:18:30 +0000 http://www.shsmaths.com/?p=1479#comment-6629 Aalia, I don't know which book you are using, but if it's Sine and Cosine rules then the triangles won't be right-angled so you shouldn't be using Pythagoras. Look at your lesson notes - there's an extra term in the cosine rule that you mustn't ignore. They don't tell you the angle because that is what the question wants you to find. The cos of an obtuse angle is negative so it's OK to get a negative number. You shouldn't, however, be trying to square-root it! Have another go and bring your attempt to someone in the department for help. JT Aalia, I don’t know which book you are using, but if it’s Sine and Cosine rules then the triangles won’t be right-angled so you shouldn’t be using Pythagoras.
Look at your lesson notes – there’s an extra term in the cosine rule that you mustn’t ignore.
They don’t tell you the angle because that is what the question wants you to find. The cos of an obtuse angle is negative so it’s OK to get a negative number. You shouldn’t, however, be trying to square-root it!
Have another go and bring your attempt to someone in the department for help.
JT

]]> By: aalia http://www.shsmaths.com/2010/03/mr-brewins-year-9-sine-and-cosine-rules/comment-page-1/#comment-6627 aalia Wed, 10 Mar 2010 18:26:31 +0000 http://www.shsmaths.com/?p=1479#comment-6627 Mr brewin, for questions e on both, they dont tell you the angle, and also for question 2. When using cosine, do you have to change the a^2=b^2+c^2 when the hyp has all ready been shown? its really confusing and i dont understand them, and on a question i got a negative answer and you cannot find the square root!! Mr brewin, for questions e on both, they dont tell you the angle, and also for question 2. When using cosine, do you have to change the a^2=b^2+c^2 when the hyp has all ready been shown? its really confusing and i dont understand them, and on a question i got a negative answer and you cannot find the square root!!

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