Orthonormal Basis and Hermitian inner product

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We can choose different bases to define different inner products. However, different orthonormal bases will generate the same inner product.

Could anyone explain the last sentence? Why different orthonormal bases give the same inner product?

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Actually, any basis defines the usual inner product in terms of coordinates, so that it actually becomes an orthonormal basis.

Now, if an inner product is given, and $b_1,\dots, b_n$ is an orthonormal basis, its inner product will coincide with the original one, because $$\left\langle\sum_i\alpha_ib_i,\, \sum_i\beta_ib_i\right\rangle\ =\ \sum_i\alpha_i\beta_i$$