Solve a quadratic with trigonometric values in degrees

[Albert Chan]

(01-28-2020 05:51 AM)Mark Hardman Wrote:  Most of that work could be eliminated if the OP recognized that cos(30) = √3/2. From there, it is only a minor mental effort to come up with d = 2500/(3*9.81). Why on earth would you need a CAS to solve that?

Same with OP

Let t = tan(x), the equation is just quadratics: -16.1*225*(1+t²) + 800*15*t = 2000
Remember that t = tan(x) have period of Pi = 180°, x have 4 solutions

d*cos(30) = 25*sqrt(d/9.81) is also a quadratics (of √d), d thus have 2 solutions.