As shown? Point A means street lamp AB means the distance MD from street lamp to straight line? NF means Xiaoming's height 1.5m? Where did Xiaoming first stand? Shadow DP= 1.5m, walk at a constant speed in DF direction for 2s to point F? That is DF=2m? PF=0.5m FC means Xiaoming's shadow =2m BD means Xiaoming's original distance.

Let AB=x? BD=y

Is it in △ABP? MD:AB=DP:BP

That is1.5: x =1.5:1.5+y? ( 1)

BC=BD+DF+FC=y+2+2=y+4

At △ABC? MF:AB=FC:BC

That is 1.5: x = 2: y+4? (2)

It is derived from equation (1) and equation (2).

1.5/( 1.5+y)=2/(y+4)

The solution is y=3.

Bring y=3 into the equation (1)? The solution is x=8.

So the height of the street lamp from the straight line is 8m.

References:

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