Question

if A+B is obtuse then what will be the value of cos(pi-(A+B))

Answer 1

Answer:

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Step-by-step explanation:

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Answer 2

Since A+B=π−C we have

tan(A+B)=tan(π−C)

⇒

1−tanAtanB

tanA+tanB

=−tanC>0 .(i)

(∵C is obtuse angle ⇒tanC<0)

Since, A and B are each less than

2π it's follows that

tanA+tanB>0

Hence (i) will hold if 1−tanAtanB>0

⇒tanAtanB<1