Calculating lengths and heights

Calculating lengths and heights

Pencil and paper
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
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Further Resources
This task is about using trigonometry to find missing lengths.
Use trigonometry to solve the following problems.
 
a)
Teresa took the ski lift 4000 metres to the top of Mount Herbert, at an angle of 40º.   
Diagram of height to ski lifts as trigonometric problem  [Not drawn to scale]
 
Calculate x, the height of Mount Herbert. Show all your working in your calculation.
 
 
x = ________ metres
 
b)
Daniel's toy boat travelled 5 metres downstream at an angle of 55° before it reached the other side of the river.   
Diagram of width of river as trigonometric problem[Not drawn to scale]
 
Calculate y the width of the river. Show all your working in your calculation.
 
 
y = ________ metres
 
c)
A penguin slid 25 metres down an iceberg at an angle of 30º until it reached the water.   
Diagram of penguins slide as trigonometric problem   [Not drawn to scale]
 
Calculate z the height of the iceberg above the water. Show all your working in your calculation.
 
 
z = ________ metres
Task administration: 
This task can be completed with pencil and paper.
Level:
5
Description of task: 
Students are required to use trigonometry to calculate the length of one side of a right-angled triangle in three problems based on a ski lift, a toy sail boat and a penguin on an iceberg.
Answers/responses: 

 

Y11 (09/2001)

a)

2571.15 (accept 2571 to 2571.15)
[full marks given even if working not shown]

Evidence of sin function (4000 sin40º), cos function (4000 cos50º) or sine rule used, but calculated incorrectly.

easy


very easy

b)

7.14 (accept 7 to 7.14)
[full marks given even if working not shown]

Evidence of tan function (5 tan55º or 5 ¸ tan35º) or sine rule used, but calculated incorrectly.

moderate


easy

c)

21.65 (accept 21 to 22)
[full marks given even if working not shown]

Evidence of cos function (25 cos30º), sin function (25 sin60º) or sine rule used, but calculated incorrectly.

easy


easy

NOTE: This item was trialled with students having access to Pythagoras' theorem and trigonometry ratios.

Diagnostic and formative information: 
  

Common error

Likely miscalculation

Likely reason

a)

 

b)


c)

6222.9

 

3.5


28.9

x =

y =

z =

Reverses opposite and hypotenuse.

 

Reverses opposite and adjacent.


Reverses adjacent and hypotenuse.

a)

3064

cos40 x 4000

Incorrect angle size used with cos function.

b)

8.7

y =

Assumes side 'y' is hypotenuse.