For positive acute angles AA and B, commaB, it is known that tangent, A, equals, start fraction, 9, divided by, 40, end fractiontanA=
40
9
​
and cosine, B, equals, start fraction, 28, divided by, 53, end fraction, .cosB=
53
28
​
. Find the value of cosine, left bracket, A, minus, B, right bracketcos(A−B) in simplest form.