Danyal124
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Can someone explain how to do these questions without cast diagramName:  image.jpg
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mqb2766
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(Original post by Danyal124)
Can someone explain how to do these questions without cast diagramName:  image.jpg
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You could use cast or sinusoidal curves or sin(A+/-B)
Which ones are you struggling with?
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Danyal124
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(Original post by mqb2766)
You could use cast or sinusoidal curves or sin(A+/-B)
Which ones are you struggling with?
The cast diagram
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mqb2766
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(Original post by Danyal124)
The cast diagram
A good way to get started with cast is just concentrate on cos(). Cos is symmetric when the angle is reflected in the x-axis and "negative symmetric" when the angle is reflected in the y-axis.

So
cos(30) = cos(-30)
as -30 is a reflection in the x-axis. Also
cos(150) = -cos(30)
as 150 is a reflection in the y axis.

See
http://mathonweb.com/help_ebook/html/cast.htm
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David Getling
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(Original post by Danyal124)
Can someone explain how to do these questions without cast diagramName:  image.jpg
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As others have said, for AS and A-level you need to learn the cast really well. This is very important.
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dextrous63
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(Original post by David Getling)
As others have said, for AS and A-level you need to learn the cast really well. This is very important.
I think part of the problem stems from students not really being taught why the cast system works, in terms of considering eg what sin(100) actually means. Since sin = opp/hyp, how is it even possible to have a right angled triangle with a 100 degree angle in it?
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David Getling
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(Original post by dextrous63)
I think part of the problem stems from students not really being taught why the cast system works, in terms of considering eg what sin(100) actually means. Since sin = opp/hyp, how is it even possible to have a right angled triangle with a 100 degree angle in it?
Sadly, you are right. I've lost count of the times I've had to go through this properly with students. And, hard as this is to believe I've even come across one or two half-wit teachers who actively discourage the use of CAST, in favour of always using graphs. Fortunately, these teachers are quite rare.
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