[dhYTvlAv]

Been lurking on this forum for many years (pre-board days) and just recently thought of a practical use I might put it to, which is not say it hasn't been useful to me in the past.
Some time ago I passed the half century and took stock of a great deal of water that had gone by the bridge and decided that there were things amiss I should put right. Having had a fine education, I had been reasonably successful in my chosen field but found there were certain capacities that, under-utilised in my youth, had atrophied and dropped off. The single most irritating one was basic trigonometry. I can recall enduring the whole rigmarole and becoming reasonably proficient at it but (because I knew better) it was something I consigned to the dustbin of the mind and no matter what I have tried in the last several years I have been unable to pick up that knack again.
In the course of my employ I became used to manipulating spreadsheets and creating simple formulas to achieve simple results. I tumbled to the fact that you could use the functions of Excel to write a spreadsheet that would calculate the angles of a triangle from the given lengths of it's elements and even wasted a not inconsiderable number of hours trying to construe such a thing by myself.
Yet it came to nothing. I'm still an ignoramus. Moreover, I feel that this shortcoming is symptomatic of something deeper and I'd like to reacquaint myself again with the more sophisticated levels of high-school mathematics that have now seized up with the rust of passing time. Without returning to high school can anyone recommend some sort of real-world/online course that I could undertake that would act as a suitable refresher? Failing that can anyone help me with the design of the spreadsheet?