# Math Help - Working out area

1. ## Working out area

ABC is a triangle

AB=8cm
BC=14cm
Angle ABC=106

Calculate the area... correct to 3 significant figures.

Even with splitting it up into right angled triangles doesn't work...

2. $A = \frac{1}{2}ac\sin(B)$

$A = \frac{1}{2}\times 14\times 8 \times \sin(106)$

3. Originally Posted by pickslides
$A = \frac{1}{2}ac\sin(B)$

$A = \frac{1}{2}\times 14\times 8 \times \sin(106)$

Please tell me the resources where you get such knowledge :/

Thank you though.

4. This calculates to -40...... can't be the area.

5. Originally Posted by Mukilab
Please tell me the resources where you get such knowledge :/

I study notes taken in classes, from books and discussions i have with colleges. The internet is also a great medium for information. Studying is great, you should try it out, it can be very rewarding.

6. Originally Posted by Mukilab
This calculates to -40...... can't be the area.
$\sin(106) > 0$ as $\forall \theta \in \{0< \theta < 180\}$ then $\sin(\theta) \geq 0$ therefore the correct answer must be positive.

7. I do study, I just find it hard to locate the correct and adequate resources. I don't know any greek signs apart from theta so if you could explain that in words....

8. Originally Posted by pickslides
$\sin(106) > 0$ as $\forall \theta \in \{0< \theta < 180\}$ then $\sin(\theta) \geq 0$ therefore the correct answer must be positive.

Originally Posted by Mukilab
I do study, I just find it hard to locate the correct and adequate resources. I don't know any greek signs apart from theta so if you could explain that in words....
The only greek letter in my statement was theta.

The statement means that for all angles between 0 and 180 sin will be positive. Therefore the result you are after must be positive as we are taking that postive result and multiplying it by only positive numbers.

9. Originally Posted by Mukilab
ABC is a triangle

AB=8cm
BC=14cm
Angle ABC=106

Calculate the area... correct to 3 significant figures.

Even with splitting it up into right angled triangles doesn't work...
Using pickslide's method I get 58.8 as an answer

10. Pickleslides, what does the upside down A mean than?

11. Originally Posted by Mukilab
Pickleslides, what does the upside down A mean than?
It means "for all"

As in for all numbers in a certain set or over an interval.

12. Har so I was right ^^

Thanks

13. How can't you split into right angled triangles??

First use cosine rule to work out the length of the remaining side = 17.94cm

Then use sine rule and basic calculation (180-angle = other angle) to work out

BCA = 25.39
CAB = 48.61

Then use use trig functions (sine and cosine) to work out length and height of triangles

And calculate the triangle with 1/2 base times height.

A = 53.8cm2

14. Originally Posted by Mukilab
Har so I was right ^^

Thanks
Right on what exactly?

Originally Posted by Mukilab
This calculates to -40...... can't be the area.
No you weren't

Originally Posted by e^(i*pi)
Using pickslide's method I get 58.8 as an answer