Hello, arangu1508!

. No!

You assumed that the diagonals of a parallelogramthe vertex angles.bisect

. . This is not true . . .

We have this parallelogram:

which gives us this triangle:Code:7x * * * * * * * * * * * 3x * * 3x * * * 60 120 * * * * * * * * 7x

Now we can use the Law of Cosines:Code:* * * __ * * 3√79 * * 3x * * * 120 * * * * * * * * 7x

. .

Got it?