First, when the dip angle is 20, the length of the slope bottom is 1×cos(20) km, and the slope height is 1×sin(20) km. After the dip angle is changed to 10, the slope height will definitely remain unchanged. At this time, the length of the slope bottom is the slope height ÷ Tan (10) km, and the elongation is the subtraction of the two slope bottom lengths, that is, sin(20)÷tan( 10)-cos(20), where the angle doubling formula sin (20) = 2 sin (/kloc-0. cos(20)=(cos( 10))^2-(sin( 10))^2； The simplified answer is 1 km.

I hope this helps.