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[Ecrofirt]

I've got a Calc 3 quiz in an hour, and I've got a question.

I have to find, correct to the nearest degree, the three angles of the triangle with verticies:
A=(1,0) B=(3,6) C=(-1,4)

We're using vectors in this chapter, and this is in the dot product area.

I tried finding the anglc between A and B by doing cos(-)=A*B/|a||B|, but I'm comoing up with 81 degrees that way, and the correct angles are supposed to be 45, 45, 90.

Can anyone help?

If I've got any more questions, I'll post them in here

 

[Slo]

I wish I could help, but Calc 3 seems soooooooooooooooooo long ago.

 

[Phantom]

Ok i think i have it

You have the 3 vertices A(1,0) B(3,6) and C(-1,4)

To work out the angle at A you need to first calculate the 2 vectors that go from A to B & C.
You just simply subtract B & C from A (2 seperate calculations) giving 2 vectors b & c (say)

now you just do cos(-) = b.c / |b||c|

I managed to get 45 degrees for angle A using that.

Hope that works for you.