trigo

lolaminx SG

from riverside prelim's 2008 paper 2:

hi guys, can someone please help me out with question b? i've got question a)'s answer(it's 25m) but my answer for is b)142.67m, which is not the same as the answer key. answer to question b is 95.4m.

4794 SG

is it me or what,i see no peektures

lolaminx SG

http://i38.tinypic.com/24zdezs.jpg here's the link!

iamapebble SG

I got a different answer from you and the answer key.. HAHA, let me try again. Meanwhile anyone who can solve it, heh heh. ^^"

Maith SG

sorry cant help oso..my ans is 133.6 which is wrong lol. wait for eagle or tintin to help!

Maith SG

tried again then get 86.6. Wrong again! lmao...u sure ur ans sheet correct?

jlzk SG

Er for part b i got...,

AH^2=200^2+100^2-2(100)(200)cos30

and i got 123.931

Feel free to correct me if i am wrong.

Maith SG

Er for part b i got...,

AH^2=200^2+100^2-2(100)(200)cos30

and i got 123.931

Feel free to correct me if i am wrong.

lol i oso got..i think the hard part to prove tht AT=95.4 tht one \:

tinuviel07 SG

200^2 = 100^2 + x^2 - 2(100)(x)cos53.8degrees

solve for X = AH.

jlzk SG

lol i oso got..i think the hard part to prove tht AT=95.4 tht one \:

i really dun quite get it wad TS asking is it for AH or to prove but if prove he will have ask how to prove ma ..so..ya.. x.x

Lee012lee SG

I work backwards,

AT = 95.4 (given)

GT = GH + HT = 50 +25 = 75 since GH = EC = 25 cm

AT^2 = AG^2 + GT^2

95.4.^2 = AG^2 + 75^2

AG = 58.96 cm

AH^2 = AG^2 + GH^2 = 58.96^2 + 25^

AH = 64 cm leh

When I work forwards,

I get the same answer as jlzk ie 123.93 cm leh.

So, does this mean that there is something wrong with the question huh ?

jlzk SG

I work backwards,

AT = 95.4 (given)

GT = GH + HT = 50 +25 = 75 since GH = EC = 25 cm

AT^2 = AG^2 + GT^2

95.4.^2 = AG^2 + 75^2

AG = 58.96 cm

AH^2 = AG^2 + GH^2 = 58.96^2 + 25^

AH = 64 cm leh

When I work forwards,

I get the same answer as jlzk ie 123.93 cm leh.

So, does this mean that there is something wrong with the question huh ?

did i did it wrongly?cause i tot u take 90-60=30 thats why get 30 .Cause first part i also treat DCB as right angle to find ..so i pressume the bottom also the same

iamapebble SG

By using sine rule the answer will be different, but by using cosine rule you get the answer, interesting..

jlzk SG

By using sine rule the answer will be different, but by using cosine rule you get the answer, interesting..

Really? Lols..i though a answer can obtain as long the method is correct ..

iamapebble SG

Really? Lols..i though a answer can obtain as long the method is correct ..

Yup, for o'levels yes. But for school papers sometimes the setter may give the answer a value that make the question logical, but end up neglecting one little part as the answer may vary or something..

But for this question, I'm not sure if it's this case or maybe cosine rule is the only method you can apply for this case? Let's wait for others to confirm :)

tinuviel07 SG

what's e answer for AH?

Lee012lee SG

what's e answer for AH?

Not sure leh,

I work backwards AH = 64 cm but I work forwards AH = 123.93 leh, same as jlkz..

May be question something wrong lah.

tinuviel07 SG

hmmm okie.. shall slowly read since i don have a calculator with me so got to use excel

eagle SG

for question b, confirm AT = 143 m (3 s.f.)

Used 2 methods to confirm.

It is definitely not 95.4 m

But then, if you don't consider the 30 degrees,
AH² + 100² - 2(AH)(100) cos 53.8 = 200²
AH² -120AH – 30000 = 0

AH = (120 +- sqrt(120² +4*30000))/2
AH = 243.3m or -123m (N.A.)

tinuviel07 SG

for question b, confirm AT = 143 m (3 s.f.)

Used 2 methods to confirm.

It is definitely not 95.4 m

Trust yourself when the question has mistakes... :D

lol i thought i wrong.. yay