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19 Nov 2011, 08:12
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Bookmarks
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
45%
(medium)
Question Stats:
57% (01:33) correct
43%
(01:27)
wrong
based on 70
sessions
History
Date
Time
Result
Not Attempted Yet
Two sides of a triangle and their included angles are 4cm, 5cm and 30 degree resp. What is the are
A 10
B 15
C 5
D 20
A 10
B 15
C 5
D 20
21 Nov 2011, 08:56
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cleetus
Take the side of length 5 as your base. When you draw a height using this base, you will get a 30-60-90 triangle with a hypotenuse of 4. Since the short side in this triangle is our height, and since the short side in a 30-60-90 triangle is half the hypotenuse, the height is 2. So the area is 5*2/2 = 5.
A bit easier to see with a diagram of course.
11 Sep 2017, 10:48
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Two sides of a triangle and their included angles are 4cm, 5cm and 30 degree resp. What is the area.
Please check attached image for detailed figure and explanation (ignore my handwriting
)
Option 1: If we see 5 and 4 as sides, we usually go with right triangle and find 3rd side with Pythagoras theorem.
so 3rd side here = 3 . And area becomes 1/2 *4*3 =6
But its wrong answer as for right triangle 3,4,5 the angle between sides 5 and 4 is not 30 degree.
(Here non of the option is 6 so most likely we will not make this mistake)
Option 2: (Check attached img for diagram)
If we consider 5cm as base, we can draw a triangle using 4cm as 1 side and angle 30degree between them .
To find height of triamgle, drop perpendicular from 4cm side on 5cm base. Height can be calculated as we know angle = 30 degree.
So height = sin30 * 4cm = 2
so Area = 1/2 *5*2 = 5
Answer: C
Option 3: Using formula
Area formula if we know 2 sides of triangle and the angle between them =>
\(Area = \frac{a*b* Sin C}{2}\)
\(Area =\frac{4*5*Sin30}{2}\)
Area = 4*5*(1/2) /2 = 5
Answer: C
Please check attached image for detailed figure and explanation (ignore my handwriting
) Option 1: If we see 5 and 4 as sides, we usually go with right triangle and find 3rd side with Pythagoras theorem.
so 3rd side here = 3 . And area becomes 1/2 *4*3 =6
But its wrong answer as for right triangle 3,4,5 the angle between sides 5 and 4 is not 30 degree.
(Here non of the option is 6 so most likely we will not make this mistake)
Option 2: (Check attached img for diagram)
If we consider 5cm as base, we can draw a triangle using 4cm as 1 side and angle 30degree between them .
To find height of triamgle, drop perpendicular from 4cm side on 5cm base. Height can be calculated as we know angle = 30 degree.
So height = sin30 * 4cm = 2
so Area = 1/2 *5*2 = 5
Answer: C
Option 3: Using formula
Area formula if we know 2 sides of triangle and the angle between them =>
\(Area = \frac{a*b* Sin C}{2}\)
\(Area =\frac{4*5*Sin30}{2}\)
Area = 4*5*(1/2) /2 = 5
Answer: C
Attachments
Triangel with sides and angle.jpg [ 1.63 MiB | Viewed 7544 times ]
