Question

If a and b are complementary ,sin a is 4/5 find Cos b​

Answer 1

`cos b=(4)/(5)`

Explanation:

It is given that: a and b are complementary.

`\therefore a + b = 90\degree\\\\\therefore a = 90\degree - b\\\\Assuming\: sin \: ratio \: on\: both\: sides\\\\sin\:a = sin(90\degree - b)\\\\\therefore (4)/(5) = sin(90\degree - b)...(\because sin\:a = (4)/(5))\\\therefore (4)/(5) =cos\:b...\{\because sin(90\degree - \theta) = cos\: \theta\} \\\\\huge\purple{\boxed{\therefore cos\:b = (4)/(5)}}\\`