Question 847408
If that question mark is supposed to be 3, then 


tan(theta) = 4/3


tan(theta) = opp/adj


so opp = 4, adj = 3


The two legs of this triangle are 4 and 3.


The hypotenuse is sqrt(4^2 + 3^2) = sqrt(25) = 5. You effectively use the Pythagorean Theorem to find the hypotenuse.


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cos(theta) = adj/hyp


cos(theta) = <font size = 5 color="red">3/5</font>


Special note: this answer of 3/5 is only true IF tan(theta) = 4/3 (ie if my initial assumption above holds up)