RS Aggarwal & V Aggarwal - Mathematics

Book: RS Aggarwal & V Aggarwal - Mathematics

Chapter: 7. Areas

Subject: Mathematics - Class 9th

Q. No. 21 of Exercise 7A

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21

Find the area of the quadrilateral ABCD in which AD = 42 cm , = 900 and is an equilateral triangle having each side equal to 26 cm. Also, find the perimeter of the quadrilateral. [Given = 1.73]

Let us consider a right triangle ABD,


By using Pythagoras theorem in this, we get


AB =


=


=


= 10 cm


We know that,


Area of triangle =


=


= 120 cm2


We also know that,


Area of an equilateral triangle BCD = sq units


=


= 292.37 cm2


Therefore,


Area of quadrilateral ABCD = Area of triangle ABD + Area of triangle BCD


= 120 + 292.37


= 412.37 cm2


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