As the picture shows, there are two paths for tourists to get down from scenic spot A to scenic spot C. One is to take a straight line from A to C, and the other is to take a cableway from A first.

∴sinA= 1？ cos2A=5 13，sinC= 1？ cos2C=45

Available sinb = sin (a+c) = sinacosc+cosasinc = 513× 35+1213× 45 = 6365.

According to sine theorem ABS Inc = AC sinb, AB = AC sinb =1260× 456365 =1040m.

That is, the length of cableway AB is equal to1040m; ;

(2)∵ AC length of mountain road 1260m, and A walks along AC at a constant speed of 50m/min.

∴ The time required for A to reach C is 126050 = 25.2 minutes.

∫ The length of cableway AB is equal to 1040m, and the cable car runs at a constant speed in a straight line at 130m/min.

∴ The time required for the cable car to go from A to B is 1040 130 = 8 minutes.

Let the walking speed of B be vm/min, and calculate BC = AC SINA SINB =1260× 5136365 = 500m by sine theorem.

It takes 500vmin to get from b to c.

Combined with the meaning of the question, 8+ 1+500v≤25.2 and the solution v≥30.9vm/min are obtained.

Accurate to an integer, the walking speed of B is at least 3 1m/min.