Question

at a certain time of the day, a person 6ft tall casts a 4ft shadow. how long is the shadow cast by a 21ft tree at the same time ?

Answer 1

This can be represented as:
You would need to prove that the triangle that is from the first person is congruent to the triangle made by the second person and then you would use a fancy proportion.

Answer 2

(I suggest looking at the angles, since that's what sun works with ;) )

Answer 3

Can you work it out now?

Answer 4

no need for angles

it's just

height/shadow = height/shadow

so

6/4 = 21/x

and solve for x

Answer 5

@Vocaloid but you didn't prove why it works. Before doing anything, you need to prove that the triangles are congruent by three angles.

Answer 6

@Vocaloid you need to show why you get something working after all.