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Qn(f):=abpn(x)dx=i=0n(abLin(xi)dx)=:wif(xi)Q_n(f) := \int_a^b p_n(x) \, dx = \sum_{i=0}^n \underbrace{\left( \int_a^b L_i^n(x_i) \, dx \right)}_{=:w_i} f(x_i)