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VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE General & Further Mathematics => Topic started by: #1procrastinator on June 30, 2011, 02:05:00 pm

Title: Find the area of this triangle..
Post by: #1procrastinator on June 30, 2011, 02:05:00 pm

...using the sine formula

This is from the Essentials textbook, Ch. 13, I think section D and question 1d

(http://img24.imageshack.us/img24/6001/trianglepx.png)

I've tried changing around the the numbers and all that but nothing gives the given answer

Title: Re: Find the area of this triangle..
Post by: kenhung123 on June 30, 2011, 02:34:20 pm

LOOOOOOOOOOOL how did you draw that??
Use sin rule to find other side then you can use Herons

Title: Re: Find the area of this triangle..
Post by: brightsky on June 30, 2011, 03:24:51 pm

no need to use heron's formula, it's an isosceles triangle so just find the altitude (which would be 5sin(15)), then multiply this by the base length (5sin(150)/sin(15)) and then halve it.

Title: Re: Find the area of this triangle..
Post by: JinXi on June 30, 2011, 03:27:31 pm

Edit : Accident Double posted :P

Title: Re: Find the area of this triangle..
Post by: JinXi on June 30, 2011, 03:29:59 pm

Quote from: JinXi on June 30, 2011, 03:27:31 pm

Since it's an isocelles triangle, 2 of the edges have a angle of 15 degree.

The 3rd angle between then 2 side lengths of 5 would be 150 degrees.

so, use the triangle formula. 0.5*(5)*(5)*sin(150)

Edit: Not sure if this method is valid for *Using the sine formula?

Title: Re: Find the area of this triangle..
Post by: kenhung123 on June 30, 2011, 03:33:13 pm

As an alternative method  ;)

Title: Re: Find the area of this triangle..
Post by: #1procrastinator on July 04, 2011, 01:08:31 pm

Thanks, but is it possible to use the sine formula (just curious)? (it doesn't say you have to use the sine formula by the way, but I assumed you should based on the examples)

Title: Re: Find the area of this triangle..
Post by: BubbleWrapMan on July 04, 2011, 05:24:22 pm

Since it's isosceles you can easily calculate the other two angles. The other base angle is also 15º which means the angle enclosed by the two equal sides is 150º. So the area is given by:

1/2 x 5 x 5 x sin(150º)