- #1
PcumP_Ravenclaw
- 106
- 4
Theorem 4.2.5 The most general linear map ## f : R^3 → R ## is of the form ## x → x·a##, for some vector a in ##R^3##.
Proof: Suppose that ##f : R^3 → R## is linear, and let ##a = (a_1, a_2, a_3)##, where ##a_1 =
f (i), a_2 = f (j), a_3 = f (k).##
Then ##f (x) = f (x_1i + x_2j + x_3k) = x_1 f (i) + x_2 f (j) + x_3 f (k) = x·a##.
My understanding
The function, f is scalar product and it takes two vectors x and a and changes them into a scalar x? why x again are they different? How did ## f(x) ## become ##f (x) = f (x_1i + x_2j + x_3k) ##?
Proof: Suppose that ##f : R^3 → R## is linear, and let ##a = (a_1, a_2, a_3)##, where ##a_1 =
f (i), a_2 = f (j), a_3 = f (k).##
Then ##f (x) = f (x_1i + x_2j + x_3k) = x_1 f (i) + x_2 f (j) + x_3 f (k) = x·a##.
My understanding
The function, f is scalar product and it takes two vectors x and a and changes them into a scalar x? why x again are they different? How did ## f(x) ## become ##f (x) = f (x_1i + x_2j + x_3k) ##?