PERIMETER AND AREA
Chapter 6, 'Perimeter and Area', introduces fundamental concepts of measuring the boundary and the space occupied by two-dimensional figures. Students learn to calculate the perimeter of polygons, specifically rectangles, squares, and triangles, using simple formulas. The chapter also delves into the concept of area, explaining how to measure the region enclosed by a closed figure. Mastering these concepts is crucial for building a strong foundation in geometry and for solving practical problems related to measurement in everyday life.
Perimeter kya hai? Polygons ka Perimeter
Perimeter matlab kisi bhi closed figure ki boundary ki total length. Simple words mein, agar aap kisi shape ke edges par chalte ho aur wapas starting point par aa jate ho, toh jitna distance cover kiya, woh uska perimeter hai.
- Polygon: Ek closed figure jo sirf straight line segments se bani ho.
- Perimeter of a Polygon: Uski saari sides ki lengths ka sum.
- Agar ek polygon ki sides
a, b, c, d, ...hain, toh uska Perimeter =a + b + c + d + .... - Perimeter ki unit length ki unit jaisi hi hoti hai, jaise
cm,m,km.
Example: Ek garden hai jiske edges par fencing karni hai. Fencing ki total length garden ka perimeter hogi.
Important Points:
- Perimeter hamesha closed figures ka hi calculate hota hai.
- Yeh ek 1-dimensional measurement hai (length).
- Units ka dhyaan rakho: agar sides cm mein hain, toh perimeter bhi cm mein hoga.
Perimeter: Kisi bhi closed figure ki boundary ki total length. Isko calculate karne ke liye, figure ki saari sides ko add kar dete hain.
Perimeter ek linear measurement hai, isliye iski units cm, m, km hoti hain, na ki cm² ya m².
Rectangle ka Perimeter
Rectangle ek four-sided closed figure hai jismein opposite sides equal aur parallel hoti hain, aur saare angles 90 degree ke hote hain.
- Properties:
- Length (
l) aur Breadth (b) hoti hai. - Opposite sides equal hoti hain.
Perimeter Calculation:
Ek rectangle ki do lengths aur do breadths hoti hain.
- Perimeter = Length + Breadth + Length + Breadth
- Perimeter =
l + b + l + b - Perimeter =
2l + 2b - Perimeter =
2 * (l + b)
Formula: Perimeter of Rectangle = 2 × (length + breadth)
Example: Agar ek rectangle ki length 10 cm aur breadth 5 cm hai, toh uska perimeter kya hoga?
- Perimeter =
2 * (10 cm + 5 cm) - Perimeter =
2 * (15 cm) - Perimeter =
30 cm
Perimeter of Rectangle (P) = 2 × (l + b) Jahan l length hai aur b breadth hai.
Agar perimeter diya ho aur ek side (length ya breadth) puchi ho, toh formula ko rearrange karke solve karo: l = (P/2) - b ya b = (P/2) - l.
Square ka Perimeter
Square bhi ek four-sided closed figure hai jismein saari sides equal hoti hain aur saare angles 90 degree ke hote hain.
- Properties:
- Saari sides equal hoti hain. Agar ek side ki length
shai, toh baaki sab ki bhishi hogi.
Perimeter Calculation:
Ek square ki chaaron sides equal hoti hain.
- Perimeter = Side + Side + Side + Side
- Perimeter =
s + s + s + s - Perimeter =
4 * s
Formula: Perimeter of Square = 4 × side
Example: Agar ek square ki side 7 cm hai, toh uska perimeter kya hoga?
- Perimeter =
4 * 7 cm - Perimeter =
28 cm
Perimeter of Square (P) = 4 × s Jahan s square ki side ki length hai.
Kabhi-kabhi students square ke perimeter ko s² likh dete hain, jo ki area ka formula hai. Perimeter hamesha linear hota hai, isliye 4s.
Triangle ka Perimeter
Triangle ek three-sided closed figure hai.
- Properties:
- Teen sides hoti hain. Let's say
a, b, c.
Perimeter Calculation:
Triangle ka perimeter uski teeno sides ki lengths ka sum hota hai.
- Perimeter = Side 1 + Side 2 + Side 3
- Perimeter =
a + b + c
Formula: Perimeter of Triangle = Sum of lengths of its three sides
Example: Ek triangle ki sides 3 cm, 4 cm aur 5 cm hain. Uska perimeter kya hoga?
- Perimeter =
3 cm + 4 cm + 5 cm - Perimeter =
12 cm
Special Case: Equilateral Triangle
- Equilateral triangle mein saari sides equal hoti hain. Agar ek side
shai, toh baaki do bhishi hongi. - Perimeter of Equilateral Triangle =
s + s + s = 3 * s
Perimeter of Triangle (P) = a + b + c Jahan a, b, c triangle ki sides ki lengths hain.
Agar triangle ki do sides aur perimeter diya ho, toh third side nikalne ke liye third side = Perimeter - (side1 + side2).
Regular Polygons ka Perimeter
Regular polygons woh closed figures hoti hain jinki saari sides equal length ki hoti hain aur saare interior angles equal hote hain.
- Examples:
- Equilateral Triangle (3 equal sides)
- Square (4 equal sides)
- Regular Pentagon (5 equal sides)
- Regular Hexagon (6 equal sides)
- Regular Octagon (8 equal sides)
Perimeter Calculation:
Kyunki regular polygon ki saari sides equal hoti hain, toh uska perimeter nikalna bahut easy hai.
- Perimeter = Number of sides × Length of one side
Formula: Perimeter of Regular Polygon = n × s Jahan n number of sides hai aur s ek side ki length hai.
Example: Ek regular pentagon ki side 6 cm hai. Uska perimeter kya hoga?
- Number of sides
(n)= 5 (pentagon) - Length of one side
(s)= 6 cm - Perimeter =
5 * 6 cm - Perimeter =
30 cm
Example: Ek regular hexagon ki side 4 cm hai. Uska perimeter kya hoga?
- Number of sides
(n)= 6 (hexagon) - Length of one side
(s)= 4 cm - Perimeter =
6 * 4 cm - Perimeter =
24 cm
Regular Polygon: Ek polygon jismein saari sides aur saare angles equal hote hain.
Perimeter of Regular Polygon (P) = n × s Jahan n number of sides hai aur s ek side ki length hai.
Area kya hai? Introduction to Area
Jab hum perimeter ki baat karte hain, toh hum boundary ki length ki baat karte hain. Lekin jab hum area ki baat karte hain, toh hum us closed figure ke andar kitni space hai, uski baat karte hain.
- Area: Kisi bhi closed figure ke andar ka region jo woh cover karti hai.
- Area ek 2-dimensional measurement hai (length × breadth).
- Area ki units hamesha square units mein hoti hain, jaise
cm²(square centimeters),m²(square meters),km²(square kilometers).
Example: Ek room mein kitni tiles lagengi, yeh us room ke floor area par depend karta hai. Ek painting kitni jagah cover karti hai wall par, woh uska area hai.
Area ko kaise samjhein?
Imagine karo ek graph paper hai jismein 1 cm × 1 cm ke squares bane hain. Agar aap us graph paper par koi shape draw karte ho, toh us shape ke andar jitne poore squares aate hain aur jitne aadhe ya usse zyada squares aate hain, unko count karke hum roughly area estimate kar sakte hain.
- Full squares: Har full square ko 1 unit count karo.
- Half squares: Har half square ko 1/2 unit count karo.
- More than half squares: Har more than half square ko 1 unit count karo.
- Less than half squares: Inko ignore kar do (0 unit count karo).
Area hamesha positive hota hai, kyunki yeh physical space ko represent karta hai.
Area: Kisi bhi closed figure ke andar ka region jo woh cover karti hai. Yeh 2-dimensional hota hai.
Area ek surface measurement hai, isliye iski units cm², m², km² hoti hain. Units ka dhyaan rakhna bahut important hai!
Rectangles aur Squares ka Area
Ab hum specific shapes, rectangle aur square, ka area calculate karna seekhenge.
Rectangle ka Area:
Ek rectangle ka area uski length aur breadth ke product ke equal hota hai.
- Properties: Length (
l) aur Breadth (b).
Area Calculation:
Imagine karo ek rectangle hai jismein l units length hai aur b units breadth hai. Agar hum isko unit squares mein divide karein, toh total squares l * b honge.
- Area = Length × Breadth
Formula: Area of Rectangle = l × b
Example: Ek rectangular field ki length 20 m aur breadth 10 m hai. Uska area kya hoga?
- Area =
20 m * 10 m - Area =
200 m²
Square ka Area:
Square ek special type ka rectangle hai jismein length aur breadth equal hoti hain (side s).
- Properties: Saari sides equal (
s).
Area Calculation:
Square ka area uski side ko ussi se multiply karke nikalta hai.
- Area = Side × Side
Formula: Area of Square = s × s = s²
Example: Ek square room ki side 8 m hai. Uska area kya hoga?
- Area =
8 m * 8 m - Area =
64 m²
Perimeter aur Area ka Relation:
- Ek hi perimeter wale shapes ka area alag-alag ho sakta hai.
- Ek hi area wale shapes ka perimeter alag-alag ho sakta hai.
Example:
- Rectangle 1:
l = 6 cm, b = 4 cm. Perimeter =2(6+4) = 20 cm. Area =6*4 = 24 cm². - Rectangle 2:
l = 7 cm, b = 3 cm. Perimeter =2(7+3) = 20 cm. Area =7*3 = 21 cm². - Yahan, perimeter same hai (20 cm), but area alag-alag hai (24 cm² vs 21 cm²).
- Rectangle 3:
l = 8 cm, b = 3 cm. Area =8*3 = 24 cm². Perimeter =2(8+3) = 22 cm. - Rectangle 4:
l = 6 cm, b = 4 cm. Area =6*4 = 24 cm². Perimeter =2(6+4) = 20 cm. - Yahan, area same hai (24 cm²), but perimeter alag-alag hai (22 cm vs 20 cm).
Area of Rectangle (A) = l × b Area of Square (A) = s × s = s²
Area aur Perimeter do alag concepts hain. Same perimeter wale shapes ka area alag ho sakta hai, aur same area wale shapes ka perimeter alag ho sakta hai. Don't confuse them!.
Triangle ka Area
Class 6 mein, hum triangle ke area ko rectangle ke area se relate karke samajhte hain. Hum directly formula derive nahi karte, but concept ko visualize karte hain.
Visualizing Area of a Triangle:
- Ek rectangle draw karo.
- Uski ek diagonal draw karo.
- Rectangle ko us diagonal ke along cut karo.
- Aapko do triangles milenge. Ye dono triangles exactly same honge (congruent) aur ek dusre ko overlap karenge.
Iska matlab hai ki, ek rectangle ko diagonal se kaatne par jo do triangles bante hain, unka area equal hota hai. Aur har triangle ka area original rectangle ke area ka aadha hota hai.
- Area of Rectangle =
l × b - Toh, Area of each Triangle =
(1/2) × (Area of Rectangle) - Area of each Triangle =
(1/2) × l × b
Is context mein, rectangle ki length (l) triangle ka base (b) ban jaati hai, aur rectangle ki breadth (b) triangle ki height (h) ban jaati hai.
Formula: Area of Triangle = (1/2) × base × height
Example: Ek triangle ka base 10 cm aur height 6 cm hai. Uska area kya hoga?
- Area =
(1/2) 10 cm 6 cm - Area =
(1/2) * 60 cm² - Area =
30 cm²
Complex Figures ka Area:
Kabhi-kabhi humein aisi figures ka area nikalna hota hai jo standard shapes (rectangle, square) nahi hoti. Aise mein, hum un figures ko chote-chote rectangles aur squares mein split kar dete hain aur phir har part ka area nikal kar unko add kar dete hain.
Steps:
- Complex figure ko simple, known shapes (rectangles, squares) mein divide karo.
- Har simple shape ka area calculate karo.
- Saare individual areas ko add kar do.
Example: Ek 'L' shaped figure hai. Isko do rectangles mein divide kar sakte hain. Phir dono rectangles ka area nikal kar add kar do.
- Important: Units ko hamesha consistent rakho. Agar ek side cm mein hai aur dusri m mein, toh pehle unko same unit mein convert karo (e.g., dono ko cm mein ya dono ko m mein).
Area of Triangle (A) = (1/2) × base × height Jahan base triangle ka base hai aur height us base ke corresponding height hai (perpendicular distance from the opposite vertex to the base).
Complex figures ka area nikalte waqt, figure ko carefully split karo. Multiple ways ho sakte hain split karne ke, but final answer same aana chahiye. Units ka conversion mat bhoolna.