
Doug C. answered 05/14/20
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Ris K.
asked 05/14/20Khrystyna and Chris are standing 300 feet away from each other on flat ground looking up at a crane. If Khrystyna’s angle of elevation to the crane is 49˚ and Chris’s is 78˚, what is the height of the crane to the nearest tenth of a foot?
Doug C. answered 05/14/20
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Yefim S. answered 05/14/20
Math Tutor with Experience
If x is horizontal distance from Khrystina to bottom of craine is, then Chris,s distance is (x - 300). If h is height of crane,then x = h/tan49° and x - 300 = h/tan78°;
From here we get equation for h: h/tan49° - 300 = h/tan78° and h = 300tan49°·tan78°/(tan78° - tan49°) ≈ 450.8 foot
When the crane is in front of Chris and Khrystyna
AB = crane's height
BC = Distance from Chris to the crane
BK = Distance from Khrystyna to the crane
Since Chris and Khrystyna are 300ft apart
so we can restate BK into
BK = BC + 300
From Chris point of view
Tan 78 = AB/BC
Tan 78 = AB/BC
AB = BC * tan 78
From Khrystyna point of view
tan 49 = AB / BK
tan 49 = AB / (BC + 300)
AB = tan 49 * (BC + 300)
AB = AB
BC * tan 78 = tan 49 (BC + 300)
BC * tan 78 = BC* tan 49 + 300 * tan 49
BC * tan 78 - BC* tan 49 = 300 * tan 49
3.554 BC = 345.110
BC = 97.097 feet
AB = BC * tan 78
= 97.097 * tan 78
= 456.8 feet
When the crane is in between Chris and Khrystyna
AB = crane's height
BC = Distance from Chris to the crane
BK = Distance from Khrystyna to the crane
Since Chris and Khrystyna are 300ft apart
so we can restate BK into
BK = 300 - BC
From Chris point of view
Tan 78 = AB/BC
Tan 78 = AB/BC
AB = BC * tan 78
From Khrystyna point of view
tan 49 = AB / BK
tan 49 = AB / (300- BC)
AB = tan 49 * (300- BC)
AB = AB
BC * tan 78 = tan 49 * (300- BC)
BC * tan 78 = 300 * tan 49 – BC * tan 49
BC * tan 78 + BC* tan 49 = 300 * tan 49
5.815 BC = 345.110
BC = 59.346 feet
AB = BC * tan 78
= 59.346 * tan 78
= 279.2 feet
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