>>226
0≦∫[0,1]{f(x)-6x+2}^2dx
=∫[0,1]{f(x)}^2dx - 12∫[0,1]xf(x)dx + 4∫[0,1]f(x)dx + ∫[0,1](36x^2-24x+4)dx
=∫[0,1]{f(x)}^2dx - 12 + 4 + 4
=∫[0,1]{f(x)}^2dx - 4

移項して
∫[0,1]{f(x)}^2dx ≧ 4