If tan A=2/3 and tan B= -3/5 what is the exact value of cot(A-B)?

cot(A-B) = 3/19

Step-by-step explanation:

The formula for cot(A-B) = (Cot A Cot B + 1 ) / (Cot B - Cot A)

we know that cot A = 1/ Tan A

Given

tan A=2/3

therefore cot A = 1/ tan A = 1/2/3 = 3/2

tan B= -3/5  

cot B = 1/ tan B = 1/-3/5 = -5/3

Thus,

(Cot A Cot B + 1 ) = (3/2)*(-5/3 )+ 1 = -5/2 +1 = (-5+2)/2 = -3/2

(Cot B - Cot A) = -5/3 -3/2 = (-5*2) + (-3*3) / 2 = -10 -9/2 = -19/2

Thus,

cot(A-B) = (Cot A Cot B + 1 ) / (Cot B - Cot A) = -3/2  / -19/2 = 3/19

Thus,

cot(A-B) = 3/19

m∠a is 90°

m∠b is 40°