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# Anyone good at maths?

I have got a really hard question in one of my assignments, and i originally failed this question in september and i got it back to re-do and i still cant do it! If anyone can help me i would be really grateful.

The question goes as follows:

In the diagram below (Fig 1)AB is the inclined jib of a crane and is 10m long. AC is 4m long. Using the sine rule, calculate the inclination of the jib to the vertical and the length of tie CB. "

The picture is here: img36.imageshack.us/img…png

i was hoping it was going to be 8+6 !?!?!?

sine is equal to opposite / hypotopomus

Original Poster

haha i wish it was as easy as that foxy!

ctuk;5524114

sine is equal to opposite / hypotopomus

thougth that only applied to a right angled triangle.

what does the "120" refer to in the picture?

Banned

If the 120 is the angle then maybe it is 120/10 * 4

Original Poster

120 is an angle so 120 degrees

Banned

Silly Old Hitler Couldn't Advance His Troops Over Asia

Sin= O/H, Cos= A/H, Tan= O/A

Banned

Silly Old Hitler Couldn't Advance His Troops Over AsiaSin= O/H, Cos= A/H, … Silly Old Hitler Couldn't Advance His Troops Over AsiaSin= O/H, Cos= A/H, Tan= O/A

I dont think you can use that hear. That is trigonometry and this requires SINE rule. I think the formula is A/a=B/b=C/c

kiwinator;5524198

120 is an angle so 120 degrees

the angle BCA = 120 degs?

a2 + b2 = c2
a2 = 16 b2 = 100 c2 = 116

sooo length CB must be = 10.770329614269007 ???

Here is the sine rule

ctuk;5524268

a2 + b2 = c2 a2 = 16 b2 = 100 c2 = 116sooo length CB must be = … a2 + b2 = c2 a2 = 16 b2 = 100 c2 = 116sooo length CB must be = 10.770329614269007 ???

If BCA is 120 degrees then CB will be shorter than AB

I'm beginning to think there maybe some info missing here

the lines CB=a, AB=c and AC=b

So the first bit you wanna find A

use c/sinC = b/sinB
10/sin120 = 4/sinB
rearrange for sinB, then find B

As you know A+B+C=180, you can find A

Now you have found A you can use c/sinC = a/SinA, where a is you're line CB

BCA isnt 120, BC-upwards is 120 ? i think

so BCA must be 60

Banned

tr2k8;5524229

I dont think you can use that hear. That is trigonometry and this … I dont think you can use that hear. That is trigonometry and this requires SINE rule. I think the formula is A/a=B/b=C/c

Ah, I can't seen the diagram here in work so can't help then

mug51;5524330

the lines CB=a, AB=c and AC=bSo the first bit you wanna find Ause c/sinC … the lines CB=a, AB=c and AC=bSo the first bit you wanna find Ause c/sinC = b/sinB10/sin120 = 4/sinBrearrange for sinB, then find BAs you know A+B+C=180, you can find ANow you have found A you can use c/sinC = a/SinA, where a is you're line CB

Mug51 has it but you need a scientific calculator which i dont posess at work

probs one online though

I drew it out based on the details & got BC = 7.5m
angle at c = 120, b = 20 & a = 40
probably wrong :whistling:

i get B to be 20.26790106 degrees, so A = 39.73209894

and CB to be 7.380831519

Mug51 has it but you need a scientific calculator which i dont posess at … Mug51 has it but you need a scientific calculator which i dont posess at work

Windows Calculator does it. Open it, then in the menu at the top, View > Scientific

J9STL;5524436

I drew it out based on the details & got BC = 7.5mangle at c = 120, b = … I drew it out based on the details & got BC = 7.5mangle at c = 120, b = 20 & a = 40 probably wrong :whistling:

lol look at the answers i got, you pretty much got my answers

mug51;5524450

i get B to be 20.26790106 degrees, so A = 39.73209894and CB to be … i get B to be 20.26790106 degrees, so A = 39.73209894and CB to be 7.380831519

Along those lines I get it to be 39.76 degrees and 7.39 m

Original Poster

Thanks for all your help guys, im gonna try and go through all the help in more detail soon