virtus
9 dots are drawn as below. How many triangles can be formed by joining three dots?



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virtus
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dw:1342275033333:dw

virtus
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@UnkleRhaukus hope your not here to troll me again

UnkleRhaukus
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thats not my style @virtus

UnkleRhaukus
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i can see four 2x2 triangles

UnkleRhaukus
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16, 1x1 triangles

UnkleRhaukus
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i suppose the dont have to be right angles

ash2326
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@virtus do you have options?

virtus
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not sure what you mean by options @ash2326 but incase you were wondering, my solution book says 9C3 8

virtus
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@UnkleRhaukus you have PARTIALLY redeemed yourself

UnkleRhaukus
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i feel better already,

virtus
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good to know, why don't you change feeling "good" to "euphoric" by suggesting why the answer is 9C3 8

UnkleRhaukus
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say you want to find all the triangle that have the top left as a vertex, how many can you make

mukushla
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9C3 triples which are in the same line=9C38
dw:1342275604359:dw

UnkleRhaukus
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i count eighteen dw:1342275638118:dw

UnkleRhaukus
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19,20dw:1342275746454:dw

UnkleRhaukus
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there are so many

virtus
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but hows that joining three dots?

UnkleRhaukus
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mukushla is right , we are misusing the straight lines because they are not triangles

mukushla
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different triangles can be formed by joining 3 of the dotes unless 3 dots are in the same line, so
C(3,9)8

virtus
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but why is do we minus 8

virtus
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*why do we

mukushla
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u can count triples of dots that are in the same line just like what i did up there

UnkleRhaukus
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this is not a triangle dw:1342276198984:dw

virtus
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oh ok

sarthak810
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