Answer:
third one
I'm assuming does 2's are squared symbols.
Step-by-step explanation:
It's the third one because
sin^2 x sec^2 x
sin^2 x (1/cos^2 x) by reciprocal identity
sin^2 x/cos^2 x by multiplicative identity prop
tan^2 x by quotient identity
The first one wouldn't work because plugging in pi/4 gives 1+1=1 which isn't true.
The second one doesn't work because plugging in pi/4 gives 2+2=1 which isn't true.
The last equation doesn't make sense at all. There is no variable on the left and on the right there is an extra variable.
