Post: Missed a maths lesson, help with the work.
01-16-2011, 03:41 PM #1
(adsbygoogle = window.adsbygoogle || []).push({}); I was off sick and missed a maths lesson in which the class found out how to work out and prove the area of a triangle with 1/2 ab Sin C.

I have looked on the internet for help with this but couldn't find something with good examples. Does anybody have any good resources for this?

Thanks Smile.
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01-16-2011, 08:13 PM #2
elfmotat
Rᵤᵥ - ½gᵤᵥR ∝ Tᵤᵥ
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Example: Let's say angle A = 60 degrees and the length of the hypotenuse is 5.

What we need to find the area of the triangle are the lengths of sides a and b.

For side a: We know that sin(A)=a/h.
Plug the values you already know into the equation:
sin(60)=a/5
Now solve for a:
5*sin(60)=a
This means the length of side a is 5*sin(60). Plug this into a calculator:
a=5*sin(60)=4.33

To find side b you can now either use the Pythagorean Theorem, or you can use the cosine function. I'll show you how using cosine:

cos(A)=b/h
cos(60)=b/5
5*cos(60)=b
b=2.5

Finding the area is simple now:
Area=(1/2)*a*b=(0.5)(4.33)(2.5)=5.4125


If you're still stuck, watch these videos:

[ame=https://www.youtube.com/watch?v=F21S9Wpi0y8]YouTube - Basic Trigonometry[/ame]
[ame=https://www.youtube.com/watch?v=QS4r_mqs-rY]YouTube - Basic Trigonometry II[/ame]

I don't want to confuse you with this, but he uses radians in his other videos:

[ame=https://www.youtube.com/watch?v=9zspW8u6kQM]YouTube - Radians and degrees[/ame]
[ame=https://www.youtube.com/watch?v=znR9tW4AiZI]YouTube - Using Trig Functions[/ame]
[ame=https://www.youtube.com/watch?v=RoXmKYjpLGk]YouTube - Using Trig Functions Part II[/ame]

The following 2 users say thank you to elfmotat for this useful post:

+tA. Rick, Leo99756
01-16-2011, 08:17 PM #3
ZoneHD
Shiver do you lift?
Didnt understand a word of both of you....

Thank god im in general Smile
01-22-2011, 12:22 AM #4
I have not had this lesson yet
01-22-2011, 12:23 AM #5
Default Avatar
-Rhys-
Guest
Elfmotat is way too smart :(
01-22-2011, 12:25 AM #6
zb4
Banned
Originally posted by Leo99756 View Post
I was off sick and missed a maths lesson in which the class found out how to work out and prove the area of a triangle with 1/2 ab Sin C.

I have looked on the internet for help with this but couldn't find something with good examples. Does anybody have any good resources for this?

Thanks Smile.


gay!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
01-22-2011, 12:27 AM #7
Naruto
Dark Knight
Just use the name of Pocahontus's sister: SOH-CAH-TOA
01-22-2011, 04:18 AM #8
Millz
Worth the Weight
Originally posted by elfmotat View Post
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Example: Let's say angle A = 60 degrees and the length of the hypotenuse is 5.

What we need to find the area of the triangle are the lengths of sides a and b.

For side a: We know that sin(A)=a/h.
Plug the values you already know into the equation:
sin(60)=a/5
Now solve for a:
5*sin(60)=a
This means the length of side a is 5*sin(60). Plug this into a calculator:
a=5*sin(60)=4.33

To find side b you can now either use the Pythagorean Theorem, or you can use the cosine function. I'll show you how using cosine:

cos(A)=b/h
cos(60)=b/5
5*cos(60)=b
b=2.5

Finding the area is simple now:
Area=(1/2)*a*b=(0.5)(4.33)(2.5)=5.4125


If you're still stuck, watch these videos:

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I don't want to confuse you with this, but he uses radians in his other videos:

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Would it be possible to explain that in English?

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