The area of a kite is given by ##A=(pq)/2##
Where ##p,q## are the two diagonals of the kite and ##A## is the area of he kite.
Let us see what happens with the area in the two conditions. ##(i)## when we double one diagonal. ##(ii)## when we double both the diagonals.
##(i)## Let ##p## and ##q## be the diagonals of the kite and ##A## be the area. Then ##A=(pq)/2##
Let us double the diagonal ##p## and let ##p’=2p##. Let the new area be denoted by ##A’## ##A’=(p’q)/2=(2pq)/2=pq##
##implies A’=pq##
We can see that the new area ##A’## is double of the initial area ##A##.
##(ii)##
Let ##a## and ##b## be the diagonals of the kite and ##B## be the area. Then ##B=(ab)/2##
Let us double the diagonals ##a## and ##b## and let ##a’=2a## and ##b’=2b##. Let the new area be denoted by ##B’## ##B’=(a’b’)/2=(2a*2b)/2=2ab##
##implies B’=2ab##
We can see that the new area ##B’## is four times of the initial area ##B##.