Preliminary mathematics marathon (4 Viewers)

fullonoob

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Re: another question

i did it diff way but same answer :D
Let X be on AP such that AX = 2cm

PQ^2 = 17^2 - 8^2
PQ = 15
 
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fullonoob

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Re: another question

i'll let 011er's answer this
if not done by 6 then ill do it, then merlin time :)
 

edmundsung

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another question

AB, CD are perpendicular chords of a circle, centre O. Prove that angle DAB = angle OAC


thxx
 

hungwell1337

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let angle DAB = X
so angle CDA = 90-X (right angled triangle)
let angle OAB = a
let angle OCD = ODC = b isosceles
let angle OAC = OCA = Y "
let the intersction of the two chords be E

now we can see triangle OAD is isosceles
angle OAD = angle ODA

a + X = 90 - X + b

rearranges into 2X = 90 - a + b

now look at triangle AEC a right angled triangle
angle ACE + angle CAE = 90

a + Y + (Y-b) = 90

rearranges into 2Y = 90 - a + b

therefore Y = X
 

findsome1

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(6+root7)/12

Expand sinxcosy + sinycosx

sinx = 2/3
Therefore cosx=1/3 (pythag for adjacent side)
cosy=3/4
Therefore siny = root7/4

Sub into the forumla and simplify.
Really?

I got this:

sin x= 2/3 (given) cos x= root5/3 (use pythagoras theorem) sin y= root 7/4 (pythagoras theorem) cos y = 3/4 (given)

sub into formula sinxcosy+cosxsiny

= 2/3 x3/4 + root35/ 12

(multiply)

= 6/12+ root 35/12

= (6+root 35)/12<!-- google_ad_section_end --></SPAN> <!-- / message --><!-- sig -->
 

fullonoob

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sinx = 2/3 cosx = root 5/3
cosy = 3/4 siny = root 7 /4
sin(x+y) = sinxcosy + sinycosx
 

fullonoob

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split cos^2x 2x into cos 2x . cos2x
product rule
did anyone do it another way?
 

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