if in triangle abc a=5 b=6 c=8 then cos a=?

Question

choices are
-1/20
11/32
25/32
53/80

Answer 1

Use the law of cosines.

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

(5)^2= (6)^2+(8)^2-2(6)(8)cosA

25= 36+64-96cosA

25=100-96cosA

-75=-96cosA

cosA= 75/96

A= .674131 radians or 38.6248 degrees

Answer 2

According to the Cosine rule: if a,b,c; the lengths of the arms of the triangle are known then the cosine of any angle can be calculated.

in your case:

cos(a) = (b^2 + c^2 - a^2)/2bc

hence cos(a) = (36 + 64 - 25)/2*6*8

cos(a) = 0.78125

or a = cos inv ( 0.78125)

a = 38.62483287305296187 in degrees.



i hope i helped you.

best answer?

Answer 3

Law of Cosines
a^2 = b^2 + c^2 - 2bc(cosA)

5^2 = 6^2 + 8^2 - 2(6 * 8)cos(A)
25 = 36 + 64 - 2(48)cos(A)
25 = 100 - 96cos(A)
-75 = -96cos(A)
(75/96) = cos(A)
cos(A) = (25/32)

ANS : cos(A) = (25/32)

Answer 4

So is it a right triangle??

So c is the hypotenuse..

cos = adjacent/hypotenuse.

the adjacent of a is 6 and its hypotenuse is 8..

so it's 6/8, so it's 3/4..

Hope you study it more on books and try to solve them on your own.. *^^*

Answer 5

i belive you are going to want to take cos a = b/c but you would take the the inverse cosine.

the rule i use is this SOHCAHTOA (sine- opposite, hypotenues; cosine- adjacent, hypotneus; and tangeny- opposite over adjacent)

Answer 6

Through SOH-CAH-TOA, I think its 6/8? check pls.