tan??

Since tan X= 3/5
Then we can draw a right angle triangle with opp. side =3 and adj.side=5.
Use Pyth.theorm,
hy. side = sq.root(3^2+5^2)=sq.root(34)

so
sinX=3/sq.root(34) and
cosX=5/sq.root(34)

then
3sinX+2cosX
=3*3/sq.root(34)+2*5/sq.root(34)
=19/sq.root(34)
=19*sq.root(34)/34

您可畫一個直角三角形，opposite side 是 3，adjacent side 是 5, 用 Pythagoras' Theorem, 找出 hypotenuse 是 √( 3² + 5² ) = √34

那問題就簡單了，sin X = 3 / √34, cos X = 5 / √34, 因為 0 < X < 90, 按照 CAST，所有sine, cosine values 都是正數

3 sin X + 2 cos X = (3 x 3 + 2 x 5) / √34 = 19 / √34