NCERT Solutions for Class 9 Maths Chapter 7: Triangles

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The NCERT Solutions for class 9 Maths Chapter 7 Triangles are included in the article below. A triangle is a closed shape with three angles, three sides, and three vertices. It has two basic formulas that help us to determine its area and perimeter.

Class 9 Maths Chapter 7 Triangles belong to Unit 4 Geometry which has a weightage of 27 marks in the Class 9 Maths Examination. Class 9 Maths Chapter 7 has the following important concepts: 

Download: NCERT Solutions for Class 9 Mathematics Chapter 7 pdf


NCERT Solutions for Class 9 Mathematics Chapter 7

The Chapter 7 Class 9 Maths are given below:

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Important Topics in Class 9 Maths Chapter 7 Triangles

Important Topics in Class 9 Maths Chapter 7 Triangles are elaborated below:

Area of Triangles

The area of a triangle is the space confined within the three sides of a triangle. For calculating its area, the base length and the height of the triangle are required.

Example: What is the formula to determine the area of a triangle?

Solution: The formula to determine the Area of a Triangle is:
Area of triangle = ½ (base x height) = ½ b x h

Perimeter of Triangles

The perimeter of a respective triangle can be defined as the sum of three sides of the triangle. For example, if a triangle has sides ABC, then the perimeter of it would be (AB + BC + AC).

  1. Perimeter of Scalene Triangle:  A + B + C
  2. Perimeter of Iosceles Triangle: 2A + B
  3. Perimeter of Equilateral Triangle: 3A

Congruency of Triangles

If two triangles have the same shape and size, then they are found congruent to one another.

Example: List all the followed criteria for congruency in a triangle.

Solution: The criteria of conguency in Triangles are: 

  • SSS (side-side-side) congruency
  • SAS (side-angle-side) congruency
  • ASA (angle-side-angle) congruency
  • AAS (angle-angle-side) congruency
  • RHS (right angle-hypotenuse-side) congruency

NCERT Solutions for Class 9 Maths Chapter 7 Exercises:

The detailed solutions for all the NCERT Solutions for Triangles under different exercises are:

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CBSE X Related Questions

  • 1.
    In the given figure, PQ is a tangent to a circle with centre \(O(-5, 3)\). If coordinates of P and Q are \((3, 1)\) and \((0, 6)\) respectively, then using distance formula, show that \(PQ \perp OQ\).


      • 2.
        If 14th term of an A.P. is 4 and its 15th term is zero, then its first term is

          • –48
          • –56
          • 56
          • 48

        • 3.
          In the given figure, two triangles ABC and PQR are shown such that \(\angle A = \angle P\) and \(\angle C = \angle R\). If \(AD \perp BC\) and \(PS \perp QR\), then prove that (i) \(\Delta ADB \sim \Delta PSQ\) (ii) \(AD \times QS = BD \times PS\).


            • 4.
              Three coins are tossed together. The probability of getting exactly two tails is

                • \(\frac{2}{8}\)
                • \(\frac{1}{2}\)
                • \(\frac{3}{8}\)
                • 1

              • 5.
                Find the missing frequencies p and q in the following frequency distribution, when sum of frequencies is 40 and mean is 19 :


                  • 6.
                    Find the H.C.F. and L.C.M. of 408 and 312.

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