Question

For an angle θ with the point (15, –8) on its terminating side, what is the value of cosine?


negative 8 over 18
15 over 17
–8
15

Answer 1

Do you know the formula for cosine?

Answer 2

@Lord_Box cosine=adjacent/hypotenuse , right?

Answer 3

Right. So if you have an angle at (15, -8) then it must go in which direction (right/left 15) and (up/down 8)

Answer 4

@Lord_Box um i still kinda dont understand how to get adjacent and hypotenuse,,, sorry

Answer 5

@Lord_Box oh, so it would be cos = 15/-8 ??

Answer 6

cos is adjacent/hypotenuse, which side is adjacent to the angle?

Answer 7

@Lord_Box so its -8/15 ????

Answer 8

Again, which side is adjacent to the angle?

Answer 9

@Lord_Box uum the 15 side thats on the x line??

Answer 10

Yes. That's adjacent. Now, how could we find the hypotenuse of a triangle with sides -8 and 15?

Answer 11

@Lord_Box umm no idea im so sorry :c

Answer 12

Are you familiar with the Pythagorean theorem?

Answer 13

@Lord_Box yeah

Answer 14

a^2 + b^2 = c^2, where c is the length of the hypotenuse. Plug in -8 and 15 for a and b.

Answer 15

@Lord_Box -8^2 + 15^2 = c^2
-64 + 225 = c^2
161 = c^2 ????

Answer 16

make sure you're squaring (-8) and not - 8

Answer 17

\[(-8)^2 = 64, - (8^2)=-64\]

Answer 18

@Lord_Box oh ok sorry

Answer 19

Try the Pythagorean theorem again

Answer 20

with (-8)^2 now? @Lord_Box

Answer 21

yes

Answer 22

@Lord_Box (-8)^2 + 15^2 = c^2
64 + 225 = c^2

Answer 23

289 = c^2 is this right so far?

Answer 24

yes

Answer 25

ok so what now?

Answer 26

@Lord_Box ??

Answer 27

What did you get for c?