Question

If θ is between 0° and 90° and tanθ = 8/7, find cosθ

A. 8√(113)
B. 7√(113)/113
C. √(113)/7
D. 8√(113)/113

Answer 1

SO i find it helpful to draw it out

Answer 2

Thats supposed to be theta
Do you understand why the two legs are 8 and 7?

Answer 3

Because that is tantheta

Answer 4

Yes so you how can you find the hypotenuse of the triangle?

Answer 5

Opposite adjacent something

Answer 6

Umm try something simpler like pythagorean theorem to find the hypotnuse

Answer 7

so do 8^2+7^2=c^2

Answer 8

so c^2 = 15^2

Answer 9

no you can't do that because you have to do the exponents first
So do (8^2) THEN add (7^2)

Answer 10

c^2 = 113?

Answer 11

Yes now to get only c, you would take the square root and it would be sqrt(113)

Answer 12

So now you would have

Answer 13

AS the third side

Answer 14

so what is the formula for cos?

Answer 15

The formula for cos is c2 = a2 + b2?

Answer 16

Umm no, cosine is adjacent/hypotenuse right?
SohCahToa, ring a bell?

Answer 17

yes yes correct

Answer 18

Right so now what is cosine of theta?

Answer 19

According to the picture

Answer 20

7/ √(113) ?

Answer 21

Yup there you go :)

Answer 22

So I guess my answer is B. then?

Answer 23

Yes because that is what you get when you rationalize it

Answer 24

Thank you good sir!

Answer 25

No problem