Posted by **Katreena** on Sunday, May 5, 2013 at 3:30am.

The longer diagonal of a parallelogram measures 62 cm and makes an angle of 30 degrees with the base. Find the area of the parallelogram if the diagonals intersect at angle of 70 degrees.

- solid mensuration -
**dlsu**, Tuesday, October 15, 2013 at 2:29am
1405

- geometry -
**drowranger766**, Wednesday, October 16, 2013 at 9:39am
Since the angle of intersection of the diagonals is 70 degrees then the other angle of intersection of the diagonals is 110 degrees.

180 = 70 + θ

where θ = the other angle of intersection

θ = 110 degrees

A parallelogram makes 4 oblique triangles. One triangle has angles : 30, 40, and 110 degrees.

Since the diagonals intersect at their midpoints, the length of a side of one oblique triangle will measure 31 degrees (which is from 62/2).

By the given values you can solve for half the length of the shorter diagonal using the law of sines.

31/sin40 = x/sin30

where x = the length of one side of the oblique triangle and also half the length of the shorter diagonal.

x = 24.11371932 cm

2(24.11371932) = 48.23 --> length of shorter diagonal

use the formula:

Area of parallelogram = (lenth of longer diagonal x lenth of shorter diagonal x sinθ)/2

where θ = angle of intersection of the two diagonals (either 70 degrees or 110 degrees)

A = ((62 cm)(48.23)sin70)/2

A = 1404.962628 or 1405 cm^2

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