two adjacent sides of a parallelogram are of length 5cm and 7cm and the diagonal connecting the ends of these sides is of length 9cm find the area of the parallelogram

Area of parallelogram ABCD = 2 × Area of triangle ABD.

Since, we have three sides of a triangle and not the altitude.

So, we cannot use the formula:

Area of triangle × Base × Height

We have to use the Heron's formula.

Area

Where,

Were a, b and c are the sides of the triangle and s is the semi perimeter.

But this formula is beyond your grade level.