k1x1+k2x2+k3x3也是AX=b的解向量,那么A(k1x1+k2x2+k3x3)=b即k1・Ax1+k2・Ax2+k3・Ax3=bk1b+k2b+k3b=b(k1+k2+k3)b=ōb为非零向量,故k1+k2+k3=1