When you are solving a right triangle, how do you know which of sin, cos or tan to use?

Answer 1

soh cah toa

sine is opposite/hyp
cos is adjacent/hyp
tan is opposite/adjacent
relative to the known angle

Answer 2

When solving a right triangle, you need to know 3 of the 6 parts. (three sides and three angles) You already know one angle, which is 90 deg.
From there, you pick sin, cos, or tan depending on what else you know. Just write down the formulas for sin, cos and tan. and see which you can fill in.

Ex. for TAN function.

Tan = Side opposite / Side adjacent. and
Side Opposite = Tan * Side adjacent and
Side Adjacent = Side opposite / Tan

(Write down the same info for Sin and Cos)

From there, you could see that if you know, or want to know, the length of the side opposite the 90 deg angle, then TAN is the wrong choice.

Again, to know which function, you need to analyze what you know, and what you want to know.

Answer 3

Labeling the angles A, B, and C, with C being the right angle, and a, b, and c being the sides opposite the angles:
sinA = a/c = cosB
cosA = b/c = sinB
tanA = a/b = cotB
a^2 + b^2 = c^2
Use the equation that leaves only one unknown.

Answer 4

It all depends on what you are given. For example, if you know the length of one side that is opposite of an angle and another side adjacent to that angle, then you will use tan. If you know a side that is adjacent to the angle and another side that is the hypotenuse, then you will use cos.

Answer 5

soh-cah-toa
to know which one to use, label the sides as opp, adj, hyp
only one of those can be a variable, pick it and the side that is given as a number

Answer 6

I do it like Phifreak does it.