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I'm having trouble with some relative velocity problems.

Example A)

A boy wishes to row across a river in the shortest possible time. He can row at 2 m/s in still water and the river is flowing at 1 m/s. At which angle (theta) should he point the bow (front) of his boat.

I tried to set up a triangle and use a trig function...but I am not getting the correct answer.

The book says that the answer is 90 degrees.

I believe the relevant equation is velocity of the boat with respect to earth = velocity of the boat with respect to water + velocity of the water respect to earth

V(be)=V(bw)+V(we)

and I solve for v(bw) since they give me 2 m/s (boat with respect to earth ?) and 1 m/s (water with repsect to earth)

Then I tried to to inverse sin of (2/ sqrt(3)) but the answer is def. not 90.