Question

If the three sides of a triangle are 4,5,6 then the cosine of the angle between the sides 4 and 15 is?

Ans:
A) 4/7
B) 5/7
C) 1/8
D) 3/16
E) 3/4

help me by showing the full process of the math..

Answer 1

@abb0t @WhisperZ @Kreep @Superdeath @-BeYourself- any help here?

Answer 2

@m&msdoodle can u help me here friend? :)

Answer 3

i have no idea.... srry

Answer 4

well... okay.... :(

Answer 5

the triangle you described is jf

Answer 6

yes than??? @Garadon_Shagan

Answer 7

Now you want angle a in terms of the sides 4 and 5 and cos.

Consider side 4=C and side 5=B and 6=A

The equation linking cos to an uneven triangle is A^2 = B^2 +C^2 - 2AC * cos a

rearranging we have cos a = (A^2 - B^2 - C^2)/-2AC
= (36 - 25 - 16)/(-2 * 6 * 4)
= (-5)/(-48)
= 5/48 which can't be simplified further which means I don't have a clue either. Sorry!

Answer 8

I made a stupid mistake!
note: -2BC cos a not BA!
A^2 = B^2 + C^2 - 2BC cos a
cos a = (-5)/(-2 * 5 * 4)
cos a = 5/40
cos a = 1/8

meaning C is your answer

Answer 9

@Garadon_Shagan thanks for the descriptive solution... i got it....