Question

In triangle abc angle b= 90 . find the value of (i)cos a cos c - sin a sin c

Answer 1

See
cos of an angle is adjacent / hypotenuse and
sin of an angle is opposite / hypotenuse

cos a = AB/AC
cos c = BC/AC
So, cos a * cos c = AB/AC*BC/AC
= AB*BC/AC^2

sin a = BC/AC
sin c = AB/AC
so, sin a * sin c = AB/AC*BC/AC
= AB*BC/AC^2
so
So the whole cuts and the ans is 1

This pic for better explanation