trigonometry maths a level question

im struggling to see where what I did was wrong? I mean, i did get a negative answer lol but my reasoning seems fine? if that makes sense.
the mark scheme did it differently to me. any help would be appreciated. thanks :smile:

WhatsApp Image 2021-01-20 at 11.35.38 AM.jpeg

Attachment not found

(edited 3 years ago)

Reply 1

mqb2766

21

Can you explain your approach a bit more? It should be reasonably straightforward?

(edited 3 years ago)

Reply 2

DFranklin

18

I can't see how your working relates to the question - are you sure you've posted the right question?

Reply 3

username3477548

OP

20

Original post by mqb2766

Can you explain your approach a bit more? It should be reasonably straightforward?

i used the sine rule to get two equations in terms of h and x. i then rearranged to get both of them in terms of x, then equated the then re-arranged to find the value of h?

Reply 4

mqb2766

21

Original post by vix.xvi

i used the sine rule to get two equations in terms of h and x. i then rearranged to get both of them in terms of x, then equated the then re-arranged to find the value of h?

But you don't seem to use 80m, why 32 and 38 degrees ....
Rather than the trig mechanics, what are you trying to find and how?

Reply 5

DFranklin

18

Note that the OP writes 12a for the question they're answering, but the attachment is for a question 6...

Reply 6

username3477548

OP

20

Original post by DFranklin

Note that the OP writes 12a for the question they're answering, but the attachment is for a question 6...

Omg tysm for pointing that out

Original post by mqb2766

But you don't seem to use 80m, why 32 and 38 degrees ....
Rather than the trig mechanics, what are you trying to find and how?

I attached the wrong photo im so sorry. Here's the correct question.

Reply 7

Muttley79

20

Original post by vix.xvi

Omg tysm for pointing that out

I attached the wrong photo im so sorry. Here's the correct question.

You've gone wrong when you multiply through as you've 'ignored' doing anything to the 15.

You seem to have made it very complicated - they are right angled triangles so you could have used tan

e.g. tan 40 = h/(x + 15) and ...

Reply 8

DFranklin

18

Original post by vix.xvi

Omg tysm for pointing that out

Your

50^o

angle seems to change to

30^o

for no obvious reason.

Your workings would be a lot simpler if you used cos <angle> instead of manually converting to sin(90 - <angle>) and you'd be less likely to make mistakes.

Even better, you could directly use tan instead of sin(angle)/sin(90-angle) as you are doing.

Reply 9

DJ Trump fan

13

Just split it into a right angle triangle and a non right angle triangle. Work out the hypotenuese of the right angled triangle by using sine rule for the non right angled triangle. You can then just use SOHCAHTOA to find the height. As someone said above, you haven't multiplied the 15 by sin52 in your working out when you rearrange. Hope this helps.

(edited 3 years ago)

Reply 10

username3477548

OP

20

Original post by DFranklin

Your

50^o

angle seems to change to

30^o

for no obvious reason.

Your workings would be a lot simpler if you used cos <angle> instead of manually converting to sin(90 - <angle>) and you'd be less likely to make mistakes.

Even better, you could directly use tan instead of sin(angle)/sin(90-angle) as you are doing.

Original post by Muttley79

You've gone wrong when you multiply through as you've 'ignored' doing anything to the 15.

You seem to have made it very complicated - they are right angled triangles so you could have used tan

e.g. tan 40 = h/(x + 15) and ...