galicia
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Me again, the worried mum.

I need help with four maths questions on behalf of my son. He has been serious ill for the past four months and to help him pass year 4 of school, and not have to repeat the whole year, I seriously need help.

The school have given him a project of 15 maths questions and he can do all but four.

Knowing that cos of A = 1/3 and that 270°<A<360° , calculate sin A and tan (without calculating the value of A).

Thanks
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MR1999
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(Original post by galicia)
Me again, the worried mum.

I need help with four maths questions on behalf of my son. He has been serious ill for the past four months and to help him pass year 4 of school, and not have to repeat the whole year, I seriously need help.

The school have given him a project of 15 maths questions and he can do all but four.

Knowing that cos of A = 1/3 and that 270°<A<360° , calculate sin A and tan (without calculating the value of A).

Thanks
Use the formulae  \sin A \equiv \sqrt{1-\cos^2 A} and  \displaystyle \tan A \equiv \frac{\sin A}{\cos A}

But since  270 ^{\circ} &lt; A &lt; 360^{\circ} , A is in the  \text{IV} quadrant, so we need to be careful of the signs of \sin A and  \tan A.
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Muttley79
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(Original post by Desmos)
Use the formulae  \sin A \equiv \sqrt{1-\cos^2 A} and  \displaystyle \tan A \equiv \frac{\sin A}{\cos A}

But since  270 ^{\circ} &lt; A &lt; 360^{\circ} , A is in the  \text{IV} quadrant, so we need to be careful of the signs of \sin A and  \tan A.
If he's in Year4 that is GCSE and so this is not appropriate.
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Muttley79
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(Original post by galicia)
Me again, the worried mum.

I need help with four maths questions on behalf of my son. He has been serious ill for the past four months and to help him pass year 4 of school, and not have to repeat the whole year, I seriously need help.

The school have given him a project of 15 maths questions and he can do all but four.

Knowing that cos of A = 1/3 and that 270°<A<360° , calculate sin A and tan (without calculating the value of A).

Thanks
Is this GCSE as you say Year 4? I'd draw a triangle with adjacent side 1 and hypotenuse 3 then you can get sine and tan - then think about CAST.

If he has been ill for so long then repeating the year might be better if he is taking GCSE next year.
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thekidwhogames
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Use CAST. It's in the fourth quadrant or the C (in CAST) as it's between 270 and 360. Make a triangle to the horizontal and call the acute angle X let's say. We know the adjacent of the triangle is 1 and the hypotenuse 3 (to satisfy CosX = 1/3). Use Pythagoras to get the opposite side to be 2 root 2. In this quadrant, tan = - 2root2 (it's negative) and sine is -2/3 root 2 (negative). Hope this helps.
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galicia
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(Original post by Muttley79)
Is this GCSE as you say Year 4? I'd draw a triangle with adjacent side 1 and hypotenuse 3 then you can get sine and tan - then think about CAST.

If he has been ill for so long then repeating the year might be better if he is taking GCSE next year.
Thanks. But he missed the last 2 months of school and will probably miss the first term if he had to repeat. He has just been diagnosed with Crohns and finally started his treatment yesterday. There is no way the Consultant will let him go to school yet as medication affects his immune system.

It is year 4 but he attends a secondary school here in Galicia NW Spain. He is going to take a year out and then the following school year will start the international baccalaureate.
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MR1999
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(Original post by Muttley79)
If he's in Year4 that is GCSE and so this is not appropriate.
Clearly he's not in year 4 of British education.
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Muttley79
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(Original post by Desmos)
Clearly he's not in year 4 of British education.
You've quoted an A level approach for a GCSE question. [year 4 of secondary I assumed]
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MR1999
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(Original post by Muttley79)
You've quoted an A level approach for a GCSE question. [year 4 of secondary I assumed]
You mentioned CAST which is first taught in C2.
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Muttley79
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Yes, that's what I assumed.
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Muttley79
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(Original post by Desmos)
You mentioned CAST which is first taught in C2.
No- it's met at GCSE where I teach,
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thekidwhogames
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(Original post by Muttley79)
Is this GCSE as you say Year 4? I'd draw a triangle with adjacent side 1 and hypotenuse 3 then you can get sine and tan - then think about CAST.

If he has been ill for so long then repeating the year might be better if he is taking GCSE next year.
CAST isn't GCSE.
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Muttley79
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(Original post by thekidwhogames)
CAST isn't GCSE.
It can be ...
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thekidwhogames
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(Original post by Muttley79)
It can be ...
No, it's not. It is nowhere in the specification and has never been in any exam. The question itself isn't GCSE.
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Muttley79
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(Original post by thekidwhogames)
No, it's not. It is nowhere in the specification and has never been in any exam. The question itself isn't GCSE.
The OP is not following a UK curriculum so it could be in their GCSE ...
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thekidwhogames
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(Original post by Muttley79)
The OP is not following a UK curriculum so it could be in their GCSE ...
But then introducing identities (trig) is fine and acceptable. If they're not following the GCSE spec, then both CAST/trig identities should be accepted.
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Muttley79
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(Original post by thekidwhogames)
But then introducing identities (trig) is fine and acceptable. If they're not following the GCSE spec, then both CAST/trig identities should be accepted.
CAST has been in GCSE and we stil teach it - trig identities have NEVER been in GCSE or O level before that.
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thekidwhogames
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(Original post by Muttley79)
CAST has been in GCSE and we stil teach it - trig identities have NEVER been in GCSE or O level before that.
GCSE refers to England/Wales in which case CAST has never been taught at GCSE. Also, the trig identities have been introduced in some books of the 9-1 GCSE Maths but it's not part of the spec. Therefore both CAST and trig identities are equally not in the GCSE so giving answers with trig identities I think is fine (not that they're needed).
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Muttley79
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(Original post by thekidwhogames)
GCSE refers to England/Wales in which case CAST has never been taught at GCSE. Also, the trig identities have been introduced in some books of the 9-1 GCSE Maths but it's not part of the spec. Therefore both CAST and trig identities are equally not in the GCSE so giving answers with trig identities I think is fine (not that they're needed).
GCSE started 30 years ago - CAST has been in the spec - we actually don't know that the OP is doing GCSE it might be iGCSE or similar. Whatever it is, trig identities won't be being taught.
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Student1191
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Doing that in year 4? Damn
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