Question

In the triangle a=5, b=7 ,c=8 then find the value of cos B/
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Answer 1

Answer:     1/2

Step-by-step explanation:

here, a = 5 ; b = 7 ; c = 8

we know, cos B = (c²+a²-b²)/ 2ac

                          = (8²+5²-7²)/(2×5×8)

                          = (64+25-49)/80

                          = 40/80

                          = 1/2

                                           

Answer 2

Answer:

40

Step-by-step explanation:

cosine rule:

b^2=a^2+c^2-2(a)(c)cosB

7^2=5^2+8^2-2(5)(8)cosB

49=25+64-80cosB

49-9=cosB

40=cosB