Height problems

Geometry Level 3

Find the height of the pyramid, wherein B = 3 0 \angle B = 30^\circ and D = 2 8 \angle D = 28^\circ , and B D = 150 f t BD = 150 ft


The answer is 204.67.

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1 solution

Jade Mijares
Nov 2, 2015

Height is adjacent to right angle. So line A B = h t a n 3 0 AB = \frac {h}{tan 30^\circ} and line A D = h t a n 2 8 AD = \frac {h}{tan28^\circ} . Using Pythagorean theorem on the base triangle,

( h t a n 2 8 ) 2 = ( h t a n 3 0 ) 2 + 15 0 2 \Bigg(\frac{h}{tan28^\circ}\Bigg)^2 = \Bigg(\frac {h}{tan30^\circ}\Bigg)^2 + 150^2 ( h 2 t a n 2 2 8 ) = ( h 2 t a n 2 3 0 ) + 15 0 2 \Bigg(\frac{h^2}{tan^{2}28^\circ}\Bigg) = \Bigg(\frac {h^2}{tan^{2}30^\circ}\Bigg) + 150^2 h 2 t a n 2 3 0 = h 2 t a n 2 2 8 + 150 t a n 2 3 0 t a n 2 2 8 h^2tan^230^\circ = h^2tan^228^\circ + 150tan^230^\circ tan^228^\circ ( t a n 2 3 0 t a n 2 2 8 ) ( h 2 ) = 150 t a n 2 3 0 t a n 2 2 8 (tan^230^\circ - tan^228^\circ)(h^2) = 150tan^230^\circ tan^228^\circ h 2 = 150 t a n 2 3 0 t a n 2 2 8 t a n 2 3 0 t a n 2 2 8 h^2 = \frac{150tan^230^\circ tan^228^\circ}{tan^230^\circ - tan^228^\circ} h = 150 t a n 2 3 0 t a n 2 2 8 t a n 2 3 0 t a n 2 2 8 h = \sqrt {\frac{150tan^230^\circ tan^228^\circ}{tan^230^\circ - tan^228^\circ}} h = 204.67 \boxed{h = 204.67}

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