formula 0.5 * b * c * sin(A) allows you to find the area of  TOPIC_SOLVED

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formula 0.5 * b * c * sin(A) allows you to find the area of

Postby theshadow on Sat Jul 18, 2009 4:27 pm

The formula 0.5 * b * c * sin(A) allows you to find the area of an obtuse triangle, where b and c are two sides of the triangle and A is the included angle.

How can I create a proof and make a diagram to show that this formula works for A acute, A right, and A obtuse?

Thank you!
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Re: formula 0.5 * b * c * sin(A) allows you to find the area of

Postby Honeysuckle588 on Sat Jul 18, 2009 7:09 pm

I oriented my triangles with the side b along the horizontal (the initial side of angle A), and the side c as the terminal side. Then, drop a perpendicular line from the end of c down to the line that b sits on. It shouldn't take long for you to determine that the length of this vertical line is csin(A).

One of the fun things about proofs is knowing what you are allowed to assume and use. If you are allowed to use the well-known fact that the area of a triangle is 0.5*(base)*height) then you're essentially done.

If you can't use that as a known fact, then there is a little more work to do.
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Re: formula 0.5 * b * c * sin(A) allows you to find the area of  TOPIC_SOLVED

Postby theshadow on Fri Jul 24, 2009 5:20 pm

Thank you. Using a set orientation was helpful.
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