Qualification > Math
C3 and C4 DOUBTS HERE!!!
Pias:
sin A= 3/5; find cos A;
after finding the value of cos A by formula, why is it that the negative value is taken of the root of the square of cos A.
Please could someone help me with that.
Darkstar3000:
How do they get 45 and 135 in question 8? I managed to get 22.5 and 112.5 but I have no idea how they got the other two values
Here is the question paper: http://www.scribd.com/doc/26846381/Edexcel-GCE-January-2010-Core-Mathematics-C3-QP (Jan 2010)
Here is the mark scheme : http://www.yourschoolmaster.com/mathematics/ks5/answers/2010web/C3_jan_2010ms.pdf
And also in question 3, why did they take their "alpha" to 4 decimal places, I took mine to 2 decimal places and my final answer has a 0.1 difference from theirs. Does this matter since they didn't state to what number of decimal places we should write alpha in ?
astarmathsandphysics:
cosec^2 2x - cot 2x =1
1+cot^2 2x -cot 2x =1
cot^2 2x -cot 2x =0
cot 2x(cot 2x -1)=0
cot 2x =0 so tan 2x =infinity so 2x =90, 90+180=270 so x=22.5,135
or cot 2x -1=0 so cot 2x =1 so tan 2x =1 so 2x=45, 45+180=225 so x=22.5,112.5
astarmathsandphysics:
3 dp because in part b they want the answer to 2 dp
Darkstar3000:
--- Quote from: astarmathsandphysics on January 19, 2011, 09:43:21 pm ---cosec^2 2x - cot 2x =1
1+cot^2 2x -cot 2x =1
cot^2 2x -cot 2x =0
cot 2x(cot 2x -1)=0
cot 2x =0 so tan 2x =infinity so 2x =90, 90+180=270 so x=22.5,135
or cot 2x -1=0 so cot 2x =1 so tan 2x =1 so 2x=45, 45+180=225 so x=22.5,112.5
--- End quote ---
how is 2x=90? That's the part I don't understand
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