Use the inner product <f,g>=integral 0 to 1 f(x)g(x) in the vector space C^0[0,1] of continuous functions on the domain [0,1] to find the orthogonal projection of f(x)=4x^2-1 onto the subspace V spanned by g(x)=x and h(x)=1. (Caution: x and 1 do not form an orthogonal basis of V.) what is the projV(f)?
Question
Use the inner product <f,g>=integral 0 to 1 f(x)g(x) in the vector space C^0[0,1] of continuous functions on the domain [0,1] to find the orthogonal projection of f(x)=4x^2-1 onto the subspace V spanned by g(x)=x and h(x)=1. (Caution: x and 1 do not form an orthogonal basis of V.) what is the projV(f)?
Solution
To find the orthogonal projection of f onto the subspace V, we first need to find the orthogonal basis of V. Given that V is spanned by g(x) = x and h(x) = 1, we can use the Gram-Schmidt process to find the orthogonal basis.
Step 1: Gram-Schmidt process Let's start with g(x) = x. We don't need to do anything to this, so our first basis vector is u1(x) = x.
Next, we subtract the projection of h onto u1 from h to get our second basis vector. The projection of h onto u1 is given by <h,u1>/<u1,u1> * u1.
Calculating the inner products, we get:
<h,u1> = ∫ from 0 to 1 (1x) dx = 1/2 <u1,u1> = ∫ from 0 to 1 (xx) dx = 1/3
So, the projection of h onto u1 is (1/2)/(1/3) * x = 3/2 * x.
Subtracting this from h, we get our second basis vector u2(x) = 1 - 3/2*x.
Step 2: Orthogonal projection of f onto V The orthogonal projection of f onto V is given by the sum of the projections of f onto each of the basis vectors of V.
The projection of f onto u1 is given by <f,u1>/<u1,u1> * u1, and the projection of f onto u2 is given by <f,u2>/<u2,u2> * u2.
Calculating the inner products, we get:
<f,u1> = ∫ from 0 to 1 ((4x^2 - 1)x) dx = 1 - 0 = 1 <u1,u1> = ∫ from 0 to 1 (xx) dx = 1/3
So, the projection of f onto u1 is 1/(1/3) * x = 3x.
<f,u2> = ∫ from 0 to 1 ((4x^2 - 1)(1 - 3/2x)) dx = 1/3 - 1 = -2/3 <u2,u2> = ∫ from 0 to 1 ((1 - 3/2x)(1 - 3/2*x)) dx = 1/3
So, the projection of f onto u2 is -2/3/(1/3) * (1 - 3/2x) = -2(1 - 3/2*x) = -2 + 3x.
Adding these together, we get the orthogonal projection of f onto V:
projV(f) = 3x - 2 + 3x = 6x - 2.
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