wrong image (Question: 111644.0 )

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suraj sharma

· started a discussion

· 1 Months ago

wrong image (Question: 111644.0 )

as mentioned in the question the angle between the sides is 60 degrees but in the explanation provided the angle between the sides is taken as 90 degrees and the angle between the side and the diagonal is taken as 60 degree, please specify the correct details.

Question:

The adjacent sides of a parallelogram are 2a and a. If the angle between sides of parallelogram is 60°, then one of the diagonals of the parallelogram is:

Options:

A) 3a

B) 2a

C) \(\sqrt[]{7}a\)

D) \(\sqrt[]{5}a\)

Solution:

Ans: (c)

Clearly

\(\angle \)ABC = 120°

From \(\triangle\)CAB,

cos B = \(\cfrac{C^2+a^2-b^2}{2ca}\)

we get

cos (180^o- 60^o) =\(\cfrac{4a^2+a^2-AC^2}{2\times2a\times a}\)

or \(-\cfrac{1}{2}=\cfrac{5a^2-AC^2}{4a^2}\)

or -2a² = 5a² - AC²

or AC²=7a²

\(\therefore AC =\sqrt{7}a\)

Knowledge Expert

· commented

· 1 Months ago

Dear Student,
We have not taken the angle as 90 , please see the image carefully.
Angle between the sides is 60 and the angle between side 2a and diagnol is 30.
Given answer is right.

Thanks and Regards
Team TR

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