Constructing a parallelogram which size is 6cm and 9cm the angle between size being 60 degree menion the diagonal

Answer 1

do you even look at what you type?

That's "sides" not "size"!
and "menion" just escapes me totally!

If the two diagonals are x and y, then using the law of cosines, and the fact that consecutive angles are supplementary,

x^2 = 6^2+9^2 - 2*6*9 cos 60°
y^2 = 6^2+9^2 - 2*6*9 cos 120°