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Finding the area under a curve using integration | PPTX
FINDING THE AREA
UNDER A CURVE
USING INTEGRATION
AS P1 MATH
BY: WILLIAM, VINCENT, WENDY
INTRODUCTION
• INTEGRATION IS ALSO CALLED ANTI-DIFFERENTIATION. THIS
MEANS THAT IT IS REVERSE DIFFERENTIATION.
• IF
𝒅𝒚
𝒅𝒙
= 𝒂𝒙 𝒏
THEN 𝒚 =
𝒂𝒙 𝒏+𝟏
𝒏+𝟏
, WHERE 𝒏 ≠ −𝟏.
EXAMPLE 1
• INTEGRATE:
• SOLUTION:
𝑑𝑦
𝑑𝑥
= 2𝑥3
− 3𝑥 + 1
𝑑𝑦
𝑑𝑥
= (2𝑥3
− 3𝑥 + 1 )𝑑𝑥
𝑦 =
2𝑥3+1
3 + 1
−
3𝑥1+1
1 + 1
+
1𝑥0+1
0 + 1
=
𝟏
𝟐
𝒙 𝟒 −
𝟑
𝟐
𝒙 𝟐 + 𝒙 + 𝒌
2𝑥3
− 3x + 1
EXAMPLE 2
• INTEGRATE:
• SOLUTION: EXPAND 2𝑥 − 3 2 = 4X2 − 12X + 9
𝑑𝑦
𝑑𝑥
= 4𝑥2 − 12𝑥 + 9 𝑑𝑥 =
4𝑥2+1
2 + 1
−
12𝑥1+1
1 + 1
+
9𝑥0+1
0 + 1
+ 𝑘
𝒚 =
𝟒𝒙 𝟑
𝟑
− 𝟔𝒙 𝟐 + 𝟗𝒙 + 𝒌
2𝑥 − 3 2
DEFINITE INTEGRATION
• WHEN WE ARE GIVEN VALUES LIKE THIS: 𝑎
𝑏
𝑓 𝑥 𝑑𝑥 , WHERE A AND B ARE THE
LIMITS OF THE INTEGRAL, THIS IS KNOWN AS DEFINITE INTEGRALS.
• EXAMPLE : −2
0
1 − 𝑡 − 𝑡2 𝑑𝑡
= 0 − [−2 −
−2 2
2
−
−2 3
3
]
=0 − −1
1
3
= 1
1
3
USE
INTEGRATION
TO FIND AREA
THE AREA UNDER A GRAPH
CAN BE FOUND BY USING THE
FORMULA…
WHERE A IS THE LOWER LIMIT
AND B IS THE UPPER LIMIT.
EXAMPLE
• FIND THE AREA UNDER THE CURVE 𝑦 = 𝑥2 + 2 IN WHICH THE AREA IS BOUNDED
BETWEEN X=2 AND X=6.
SOLUTION
𝐴 = 𝑎
𝑏
𝑓 𝑥 𝑑𝑥 X = 2 X = 6
𝐴 =
2
6
𝑥2 + 2 𝑑𝑥 =
2
6
𝑥2+1
2 + 1
+
2𝑥0+1
0 + 1
𝐴 =
2
6
𝑥3
3
+
2𝑥
1
=
2
6
1
3
𝑥3 + 2𝑥
𝐴 =
1
3
6 3
+ 2 6 −
1
3
2 3
+ 2 2
𝐴 = 72 + 12 −
8
3
+ 4 = 77.3
AREA UNDER THE X-AXIS
• IF A CURVE LIES BELOW THE X-AXIS, THE AREA BETWEEN THAT PART AND THE
X-AXIS IS
− 𝑦 𝑑𝑥
EXAMPLE
• THE CURVE 𝑦 = 𝑥2 − 3𝑥 + 2 = (𝑥 − 2)(𝑥 − 1) MEET THE X-AXIS WHERE X=1 AND
X=2.
FIND THE SHADED AREA.
SOLUTION
• 𝑦 𝑑𝑥 WILL HAVE A NEGATIVE DOMAIN.
• REMEMBER 𝑎
𝑏
𝑓 𝑥 𝑑𝑥
• 1
2
𝑦 𝑑𝑥 = 1
2
𝑥2 − 3𝑥 + 2 𝑑𝑥 = [
𝑥3
3
−
3𝑥2
2
+ 2𝑥]
= (
8
3
− 6 + 4) − (
1
3
−
3
2
+ 2)
=
2
3
−
5
6
= −
1
6
THIS IS THE AREA BELOW THE X-AXIS.
ANOTHER TYPE OF CURVE…
• IF A CURVE LIES PARTLY ABOVE AND PARTLY BELOW THE X-AXIS, THE TOTAL
AREA WILL BE
𝑎
𝑏
𝑦 𝑑𝑥 −
𝑏
𝑐
𝑦 𝑑𝑥
AREA BETWEEN A CURVE AND THE Y-AXIS
• THE GRAPH SHOWS THE PART OF THE CURVE 𝑦 − 1 2 = 𝑥 − 1 , FIND THE AREA
OF THE SHADED REGION.
SOLUTION
• FIRSTLY, MAKE X THE SUBJECT OF THE EQUATION OF THE CURVE.
𝑥 = 𝑦 − 1 2 + 1 = 𝑦2 + 2𝑦 + 2
FIND THE AREA 0
1
𝑦2 + 2𝑦 + 2 𝑑𝑦 =
𝑦3
3
− 𝑦2 + 2𝑦
0
1
=
1
3
− 1 + 2 − 0 = 1
1
3
𝑢𝑛𝑖𝑡𝑠2
QUESTION???

Finding the area under a curve using integration

  • 1.
    FINDING THE AREA UNDERA CURVE USING INTEGRATION AS P1 MATH BY: WILLIAM, VINCENT, WENDY
  • 2.
    INTRODUCTION • INTEGRATION ISALSO CALLED ANTI-DIFFERENTIATION. THIS MEANS THAT IT IS REVERSE DIFFERENTIATION. • IF 𝒅𝒚 𝒅𝒙 = 𝒂𝒙 𝒏 THEN 𝒚 = 𝒂𝒙 𝒏+𝟏 𝒏+𝟏 , WHERE 𝒏 ≠ −𝟏.
  • 3.
    EXAMPLE 1 • INTEGRATE: •SOLUTION: 𝑑𝑦 𝑑𝑥 = 2𝑥3 − 3𝑥 + 1 𝑑𝑦 𝑑𝑥 = (2𝑥3 − 3𝑥 + 1 )𝑑𝑥 𝑦 = 2𝑥3+1 3 + 1 − 3𝑥1+1 1 + 1 + 1𝑥0+1 0 + 1 = 𝟏 𝟐 𝒙 𝟒 − 𝟑 𝟐 𝒙 𝟐 + 𝒙 + 𝒌 2𝑥3 − 3x + 1
  • 4.
    EXAMPLE 2 • INTEGRATE: •SOLUTION: EXPAND 2𝑥 − 3 2 = 4X2 − 12X + 9 𝑑𝑦 𝑑𝑥 = 4𝑥2 − 12𝑥 + 9 𝑑𝑥 = 4𝑥2+1 2 + 1 − 12𝑥1+1 1 + 1 + 9𝑥0+1 0 + 1 + 𝑘 𝒚 = 𝟒𝒙 𝟑 𝟑 − 𝟔𝒙 𝟐 + 𝟗𝒙 + 𝒌 2𝑥 − 3 2
  • 5.
    DEFINITE INTEGRATION • WHENWE ARE GIVEN VALUES LIKE THIS: 𝑎 𝑏 𝑓 𝑥 𝑑𝑥 , WHERE A AND B ARE THE LIMITS OF THE INTEGRAL, THIS IS KNOWN AS DEFINITE INTEGRALS. • EXAMPLE : −2 0 1 − 𝑡 − 𝑡2 𝑑𝑡 = 0 − [−2 − −2 2 2 − −2 3 3 ] =0 − −1 1 3 = 1 1 3
  • 6.
    USE INTEGRATION TO FIND AREA THEAREA UNDER A GRAPH CAN BE FOUND BY USING THE FORMULA… WHERE A IS THE LOWER LIMIT AND B IS THE UPPER LIMIT.
  • 7.
    EXAMPLE • FIND THEAREA UNDER THE CURVE 𝑦 = 𝑥2 + 2 IN WHICH THE AREA IS BOUNDED BETWEEN X=2 AND X=6.
  • 8.
    SOLUTION 𝐴 = 𝑎 𝑏 𝑓𝑥 𝑑𝑥 X = 2 X = 6 𝐴 = 2 6 𝑥2 + 2 𝑑𝑥 = 2 6 𝑥2+1 2 + 1 + 2𝑥0+1 0 + 1 𝐴 = 2 6 𝑥3 3 + 2𝑥 1 = 2 6 1 3 𝑥3 + 2𝑥 𝐴 = 1 3 6 3 + 2 6 − 1 3 2 3 + 2 2 𝐴 = 72 + 12 − 8 3 + 4 = 77.3
  • 9.
    AREA UNDER THEX-AXIS • IF A CURVE LIES BELOW THE X-AXIS, THE AREA BETWEEN THAT PART AND THE X-AXIS IS − 𝑦 𝑑𝑥
  • 10.
    EXAMPLE • THE CURVE𝑦 = 𝑥2 − 3𝑥 + 2 = (𝑥 − 2)(𝑥 − 1) MEET THE X-AXIS WHERE X=1 AND X=2. FIND THE SHADED AREA.
  • 11.
    SOLUTION • 𝑦 𝑑𝑥WILL HAVE A NEGATIVE DOMAIN. • REMEMBER 𝑎 𝑏 𝑓 𝑥 𝑑𝑥 • 1 2 𝑦 𝑑𝑥 = 1 2 𝑥2 − 3𝑥 + 2 𝑑𝑥 = [ 𝑥3 3 − 3𝑥2 2 + 2𝑥] = ( 8 3 − 6 + 4) − ( 1 3 − 3 2 + 2) = 2 3 − 5 6 = − 1 6 THIS IS THE AREA BELOW THE X-AXIS.
  • 12.
    ANOTHER TYPE OFCURVE… • IF A CURVE LIES PARTLY ABOVE AND PARTLY BELOW THE X-AXIS, THE TOTAL AREA WILL BE 𝑎 𝑏 𝑦 𝑑𝑥 − 𝑏 𝑐 𝑦 𝑑𝑥
  • 13.
    AREA BETWEEN ACURVE AND THE Y-AXIS • THE GRAPH SHOWS THE PART OF THE CURVE 𝑦 − 1 2 = 𝑥 − 1 , FIND THE AREA OF THE SHADED REGION.
  • 14.
    SOLUTION • FIRSTLY, MAKEX THE SUBJECT OF THE EQUATION OF THE CURVE. 𝑥 = 𝑦 − 1 2 + 1 = 𝑦2 + 2𝑦 + 2 FIND THE AREA 0 1 𝑦2 + 2𝑦 + 2 𝑑𝑦 = 𝑦3 3 − 𝑦2 + 2𝑦 0 1 = 1 3 − 1 + 2 − 0 = 1 1 3 𝑢𝑛𝑖𝑡𝑠2
  • 15.