You have a right triangle here
The Very First thing you should do is make a sketch!!
Then you will see that the adjacent side to S is 5 and that the hypotenuse is 10
Now you can find the cos(S) = adj/hyp = 5/10
The tangent is = sin/cos or = opp/adj
The opposite side from R is the adj side to S or ST = 5
You need to find the adjacent side to R
You need Pythagorean Theorem to do that. hyp = RS
RS^2 = ST^2 + RT^2
10^2 = 5^2 + RT^2
RT^2 = 10^2 - 5^2 =
RT = √( 10^2 - 5^2 )
Now you can figure out the tan(R) = opp/adj = 5/RT
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