Deepa makes use of the geometric property of similar triangles formed by
incident and reflected rays to determine the height of the goalpost.
Reasons:
When an object is reflected on a mirror, the angle of incidence, θ₁ is equal
to the angle of reflection, θ₂.
θ₁ = θ₂
Given that the angle, ∅₁, the incident ray of light and the angle, ∅₂, the
reflected light make with horizontal are both complementary angles, to the
angle of incident and reflection, respectively, we have;
θ₁ + ∅₁ = θ₂ + ∅₂
θ₁ = θ₂
Therefore, by subtraction property of equality, we have;
∅₁ = ∅₂
The vertical line from the top of the goalpost to the base of the goalpost
and the the vertical line from Deepa's eyes to the ground on which her feet
is standing are both perpendicular to the ground, therefore, the light from
the top of the goalpost to the mirror and to her eyes form similar triangles
by Angle Angle similarity postulate, which gives;
[tex]\displaystyle \frac{6.95}{9.35} = \frac{1.35}{The \ height \ of \ the \ goalpost}[/tex]
6.95 × Height of the goalpost = 1.35 × 9.35
[tex]\displaystyle Height \ of \ the \ goalpost = \frac{1.35 \ m \times 9.35 \ m}{6.95 \ m} \approx 1.82 \ m[/tex]
The height of the goalpost is approximately 1.82 meters.
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