解y=-0.1x²+2.6x+43
=-0.1(x²-26x)+43
=-0.1[x^2-26x+13^2-13^2]+43
=-0.1[(x-13)^2-169]+43
=-0.1(x-13)^2+16.9+43
=-0.1(x-13)^2+59.9.