h(1)=ln(a+b)
M点坐标(1,ln(a+b))
h'(x)=a/(ax+b)=a/(a+b)
切线方程为：
y-ln(a+b)=a/(a+b)*(x-1)
x-1=(b/a+1)*y-(b/a+1)*ln(a+b)
x-(b/a+1)*y+(b/a+1)*ln(a+b)-1=0
(b/a+1)=2--->a=b
(b/a+1)*ln(a+b)=ln4
2ln(a+b)=4
ln(a+b)=2
a=b=1