FACTS  AND  FORMULAE  FOR  AREA  QUESTIONS

 

 

FUNDAMENTAL CONCEPTS :

I. Results on Triangles:

1. Sum of the angles of  a triangle is 180o

2. The sum of any two sides of a triangle is greater than the third side.

3. Pythagoras Theorem : In a right - angled triangle,

Hypotenuse2=Base2+Height2

4. The line joining the mid-point of a side of a triangle to the opposite vertex is called the median.

5. The point where the three medians of a triangle meet, is called Centroid. The centroid divides each of the medians in the ratio 2 : 1.

6. In an Isosceles triangle, the altitude from the vertex bisects the base.

7. The median of a triangle divides it into two triangles of the same area.

8. The area of the triangle formed by joining the mid-points of the sides of a given triangle is one-fourth of the area of the given triangle.

 

II.Results on Quadrilaterals :


1. The diagonals of a parallelogram bisect each other

2. Each diagonal of a parallelogram divides it into two triangles of the same area.

3. The diagonals of a rectangle are equal and bisect each other.

4. The diagonals of a square are equal and bisect each other at right angles

5. The diagonals of a rhombus are unequal and bisect each other at right angles

6. A parallelogram and a rectangle on the same base and between the same parallels are equal in area.

7. Of all the parallelogram of given sides, the parallelogram which is a rectangle has the greatest area.

 

IMPORTANT FORMULAE

I. 

1. Area of a rectangle = (length x Breadth)

Length =AreaBreadth  and  Breadth=AreaLength

2. Perimeter of a rectangle = 2( length + Breadth)

 

 

II. Area of square = side2=12diagonal2 

 

III. Area of 4 walls of a room = 2(Length + Breadth) x Height

 

 

IV.

1. Area of a triangle =12×base×height

2. Area of a triangle = s(s-a)(s-b)(s-c), where a, b, c are the sides of the triangle and s=12a+b+c

3. Area of an equilateral triangle =34×side2

4. Radius of incircle of an equilateral triangle of side a=a23

5. Radius of circumcircle of an equilateral triangle of side a=a3

6. Radius of incircle of a triangle of area  and semi-perimeter s=s

 

 

V.

1. Area of a parallelogram = (Base x Height)

2. Area of a rhombus = 12×Product of diagonals

3. Area of a trapezium = 12×(sum of parallel sides)×distance between them

    

 

VI.

1. Area of a cicle = πR2, where R is the radius.

2. Circumference of a circle = 2πR.

3. Length of an arc = 2πRθ360, where θ is the central angle.

4. Area of a sector = 12arc×R=πR2θ360 

 

VII.

1. Area of a semi-circle = πR22

2. Circumference of a semi - circle = πR

Q:

What is the area of this trapezoidal garden? (All measurements are in cm)

 

A) 60 sq.cm B) 180 sq.cm
C) 210 sq.cm D) 240 sq.cm
 
Answer & Explanation Answer: D) 240 sq.cm

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Q:

∆ABC is right angled at B. If cosA = 8/17, then what is the value of cotC ?

 

A)  15/8 B) 15/17
C)  8/17 D) 17/15
 
Answer & Explanation Answer: A)  15/8

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Q:

The curved surface area and the diameter of a right circular cylinder are 660 sq.cm and 21 cm respectively. Find its height (in cm).

 

A) 9 B)  10
C) 12 D) 8
 
Answer & Explanation Answer: B)  10

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Q:

If the measure of the interior angle of a regular polygon is 1800, then how many sides does it have?

 

A)  6 B) 8
C) 9 D) 5
 
Answer & Explanation Answer: D) 5

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Q:

The sum of the lengths of the edges of a cube is equal to the perimeter of a square. If the numerical value of the volume of the cube is equal to the numerical value of the area of the square, then the length of one side of the square is

A) 30 units B) 9 units
C) 27 units D) 12 units
 
Answer & Explanation Answer: C) 27 units

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Q:

A square ground is to be covered by planting 100 saplings on each side. How many saplings are needed in all?

 

A) 400 B) 404
C) 396 D) 408
 
Answer & Explanation Answer: C) 396

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Q:

Find the curved surface area (in cm2) of a right circular cone of diameter 28 cm and slant height 12 cm.

 

A)  792 B) 728
C)  528 D)  493
 
Answer & Explanation Answer: C)  528

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Q:

In ΔABC measure of angle B is 900. If cotA = 8/15, and AB = 0.8cm, then what is the length (in cm) of side BC?

 

A) 1.7 B)  2
C)  1.5 D)  2.5
 
Answer & Explanation Answer: C)  1.5

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