# A problem in Elementary Differential Geometry

My teacher has defined $U_1 = \langle1, 0, 0\rangle$, $U_2 = \langle0, 1, 0\rangle$, and $U_3 = \langle0, 0, 1\rangle$.

So it seems like the function maps $L(\langle1, 0, 0\rangle, \langle0, 1, 0\rangle) = a, L(\langle1, 0, 0\rangle, \langle0, 0, 1\rangle) = b,$, and $L(\langle0, 1, 0\rangle, \langle0, 0, 1\rangle) = c$

I'm not sure how that helps me determine what $L(\langle v_1, v_2, v_3\rangle, \langle w_1, w_2, w_3\rangle)$ is.

Could the function perhaps be $L(u, v) = L(\langle v_1, v_2, v_3\rangle, \langle w_1, w_2, w_3\rangle) = a\cdot{}v_1 + b\cdot{}w_3 + c\cdot{}v_2$

That seems to satisfy our initial conditions.

My textbook doesn't cover this and my teacher hasn't shown an example of how these functions work, so I'm unsure what to do.

Mark44
Mentor

My teacher has defined $U_1 = \langle1, 0, 0\rangle$, $U_2 = \langle0, 1, 0\rangle$, and $U_3 = \langle0, 0, 1\rangle$.

So it seems like the function maps $L(\langle1, 0, 0\rangle, \langle0, 1, 0\rangle) = a, L(\langle1, 0, 0\rangle, \langle0, 0, 1\rangle) = b,$, and $L(\langle0, 1, 0\rangle, \langle0, 0, 1\rangle) = c$

I'm not sure how that helps me determine what $L(\langle v_1, v_2, v_3\rangle, \langle w_1, w_2, w_3\rangle)$ is.

Could the function perhaps be $L(u, v) = L(\langle v_1, v_2, v_3\rangle, \langle w_1, w_2, w_3\rangle) = a\cdot{}v_1 + b\cdot{}w_3 + c\cdot{}v_2$

That seems to satisfy our initial conditions.

My textbook doesn't cover this and my teacher hasn't shown an example of how these functions work, so I'm unsure what to do.

The next thing to do would be to note that v = <v1, v2, v3> = v1U1 + v2U2 + v3U3. You can write w in a similar fashion, as a linear combination of U1, U2, and U3.

That's a start...

Dick