Question

Cos (a+b) =4/5 cos (a-b)=?​

Answer 1

Answer:

c=6

Step-by-step explanation:

Given, a=5,b=4,cos(A−B)=

32

31

Therefore, tan(

2

A−B

)=

1+cos(A+B)

1−cos(A−B)

=

63

1

⇒

a+b

a−b

cot

2

C

=

63

1

⇒

5+4

5−4

cot

2

C

=

63

1

⇒tan

2

C

=

3

7

Now, cosC=

1+tan

2

2

C

1−tan

2

2

C

⇒cosC=

1+

9

7

1−

9

7

=

8

1

Now, c

2

=a

2

+b

2

−2abcosC

⇒c

2

=25+16−40×

8

1

=36

⇒c=6