A boy stands 1 meter away from a lamppost. He is 1.8 meters tall and casts a shadow 2 meters long in the light from the lamp. Ho
w tall is the lamppost?
2 answers:
A boy stands 1 meter away from a lamppost. He is 1.8 meters tall and casts a shadow 2 meters long in the light from the lamp
The diagram is attached below using the given information
We have two similar triangle
Triangle ACD is similar to triangle ABE. So the sides are in proportional
AC = AB + BC = 3m
2x = 1.8 * 3 (cross multiply)
2x = 5.4
Divide by 2 on both sides
x = 2.7
Height of Lamppost is 2.7 meter
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u = 10.4 and v = 12
Solution:
In the given 2 sides of a triangle are 60°, 60°.
Sum of all the angles of a triangle = 180°
60° + 60° + third angle = 180°
⇒ third angle = 180° – 60° – 60°
⇒ third angle = 60°
All angles are equal, therefore the given triangle is an equilateral triangle.
⇒ All sides are equal in length.
⇒ v = 12
The line drawn from the top angle divides the triangle into two equal parts
and the line is perpendicular.
12 ÷ 2 = 6
Using Pythagoras theorem,
⇒
⇒
⇒
⇒
⇒ u = 10.4
Hence, u = 10.4 and v = 12.
So it is the product of
And 2,5 and 11 are prime numbers, so there you go :)