Math
posted by Dipankar .
If 1cosA=5/13, prove that 25sinA(sinA  cosA)

if 1  cosA = 5/13
then cosA = 15/13 = 12/13
A could be in I or IV
For I:
cosA = 12/13
then sinA = 5/13
25sinA(sinAcosA_ = 25(5/13)(5/13  12/13)
= ...
for IV
cosA = 12/13
then sinA = 5/13
25sinA(sinA  cosA)
= 25(5/13)(5/13  12/13)
= ....
I will leave the arithmetic up to you