`A=(cos^2 17^\circ+2cos^2 73^\circ)/(cot65^\circ.cot25^\circ)-sin^2 17^\circ`
`A=(cos^2 17^\circ+2sin^2 17^\circ)/(tan25^\circ.cot25^\circ)-sin^2 17^\circ`
`A=((sin^2 17^\circ+cos^2 17^\circ)+sin^2 17^\circ)/1-sin^2 17^\circ`
`A=1+sin^2 17^\circ-sin^2 17^\circ`
`A=1`
Vậy `A=1`