# bilinear form and quotient [closed]

Hi please can someone help me $$(A <, >)$$ a flat pseudo-euclidien Lie algebra which contains bilateral ideal I and also its orthogonal is bilateral ideal.

I don't understand why: if The restriction of $$<,>$$, to $$I^{\perp}$$ is degenerate have radical=I. So $$<,>_{I^{\perp} \times I^{\perp}}$$ defined by passing to the quotient a non-degenerate symmetric bilinear form on $$B=I^{\perp} / I$$