# Define on $P3$ the inner product $<f,g>=\int_{-1}^1 f(t)g(t)dt$, find orthogonal projection

by Anqi Luo   Last Updated November 18, 2018 18:20 PM

Define on $$P3$$ the inner product $$\langle f,g \rangle=\int_{-1}^1 f(t)g(t)dt$$.

a) find the orthogonal projection of $$p(x)=x^3$$ onto $$P2$$

I know the orthogonal projection formula, but how do I solve it without knowing $$f(t)$$ and $$g(t)$$?

I also have a hard time in turns of proving the Positive Definite Property of this inner product.

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