Mathamania discussion
geometry
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message 1:
by
Priya
(new)
Jan 27, 2009 08:44PM
prove the conv. of the triangle proportionality thm... =)
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Okay, I'm going to give it a try. Not promising it will make sense... =DConverse of the Triangle Proportionality Theorem:
If a line divides two sides of a triangle
proportionally, then it is parallel to the third side.
Proof:
In order for a line to divide two sides a triangle proportionally, it must create two overlapped similar triangles. For the triangles to be similar (proportional) they're angles must be equal. If all the angles are equal then the line must be parallel to the third side of the triangle.
For example: In order to divide a right triangle proportionally, the line must create another 90 degree angle (along with the other angles). The only way to get a 90 degree angle is to have a straight line intersect a straight line. The intersecting straight line then, must be parallel to one or the other straight lines of the right triangle.
Mod
Oh, and did I do any good explaining it? It's really hard without a diagram.
Mod
Yay! Thanks Joon! =DYes, we are going to have so much fun doing really hard problems! I thrive on puzzles! The only bad part is that, when faced with a puzzle/problem, it sort of takes over my brain (or is, at least, annoyingly naggy) until I know the answer. :)
Alright, here's another one:The radius of the circle is 12cm. There is an angle like this < (angle ABC) in the circle, but it does NOT pass through the center of the circle and who's inner angle is 40 degrees. Find the length of arc ABC. Round the answer to the nearest hundredth. (Again, this would be much easier if I was able to post a diagram.)
when i say prove, i mean using theorems
Sorry, but you did say to prove the theorem.
let's not be to harsh to others. She didn't know it
Elaine, what grade are you in? and what mathe course do you take in school?yejin--how was spicewood?
Why? Sorry, but I don't feel comfortable sharing that information.
Mod
me, too. The songs and i memorized every single word we said even other people's words in woodwind quintet.
Is geometry the whole shapes stuff? x
Yep. Definition for Geometry:
the branch of mathematics dealing with the properties, measurements, and relationships of points, lines, planes, and solids.
Sorry, I was curious. =)
Mod
Oooo in england we don't really categorize them into geometry, algebra ect x
Mod
We have different sections. This section i'm doing now has algebra, quadratic graphs, Surds, and some more stuff. Do you do GCSEs?
what are Surds? sorry, i have never heard of them
surds are like √20 is a surd because the number is not whole.
but say √8 simplified is √4 x √2 which is written like this: 2√2
It's hard to explain on a computer.
Nope, I get it. That's interesting that it's its own section.
Mod
Yeah! And you like add, divide, subtract-ect them.But for my non-calculator exam I had to find √20
I was like huh??
Elaine wrote: "Alright, here's another one:The radius of the circle is 12cm. There is an angle like this < (angle ABC) in the circle, but it does NOT pass through the center of the circle and who's inner angle is 40 degrees. Find the length of arc ABC. Round the answer to the nearest hundredth. (Again, this would be much easier if I was able to post a diagram.)
No one has answered my question yet!!!
Elaine wrote: "Elaine wrote: "Alright, here's another one:The radius of the circle is 12cm. There is an angle like this
No one has answered my question yet!!!
"
i agree with you...i don't rly get the question b/c idk how the diagram looks like.....i wish we could make a diagrams on computers
First should know that if I used 80 because that is the degree measure of arc ABC, and if the radius is 12cm, then the circumference is (diameter times pi) 75.36.
Then you can cross multiply to get 80(75.36)=360x. 6028.8=360x.
x (or the length of the arc) = 16.75 cm. Am I correct?
OK time for aa coordinate geometry question....Easy one to start:
Find the midpoint of the line AB when A(3,8) and B (9,-6).
