Just apply the distance formula for points (a cos〖25°,0〗 ) and (0,a cos〖65°〗 )
= √([(a Cos25-0)^2+(0-a COs65)^2 ] )
= √([a^2 Cos^2 25+a^2 Cos^2 65] )
(When we take a^2 and taking it out of the root, it will give a)
a×√((Cos^2 25+Cos^2 65) )
(We know that by complimentary angles, Cos25=Sin65, SimilarlyCos^2 25=Sin^2 65)
a×√((Sin^2 65+Cos^2 65) )
(We know thatSin^2 X+Cos^2 X=1)
a×√((1) )
√1=1
a×1=a