x_1\left(0\right)=1,\, x_1\left(\frac{\pi}{2}\right)=0,\ x_2\left(0\right)=0,\, x_2\left(\frac{\pi}{2}\right)=1,\ x_3\left(0\right)=0,\, x_3\left(\frac{\pi}{2}\right)=-\frac{\pi^2}{8}