And realizing that requires knowing some trig AND some calc.
ie, they're "easy trick questions", but only if you know the tricks."sin(60*pi*t)" is home AC, more or less, so perhaps the questions are relevant outside of "signal processing."
I actually went to
https://www.symbolab.com and stuffed in '7*cos(60 * pi * 4)'. The '4' because the problem specifies t=4. It came back 7. The first part really is 'plug and crunch'.
The second part does take a smattering of calculus. When you try to take the derivative of 7 * cos(240 * pi) to get di/dt, Symbolab gives 0 because 7 * cos(240 * pi) is a constant (because t was a constant = 4) and the derivative of a constant is 0. Or you could do it with slope...
Yes, I actually used Symbolab to get the answers. Yes, it takes a wee bit of trig and calculus. I'm not sure why the problems show up in a DC Circuit Analysis course but I don't see how you could spend an entire semester with batteries and resistors.
The thing is, I don't need to be some kind of wizard to work these problems. There are tools in the realm that make it easy. You do have to a) know about the tools and b) know which question to ask and how.
Note that when plotting this 7*cos(60*pi*x) function with Desmos, the X-axis probably wants to just go from -1 to, say, 3 and then click 'Degrees'. The 60 * pi is ok but it fills the screen with ink unless the scale is expanded. Use the wrench in the upper right corner and set the x-axis as described.
https://www.desmos.com/These are the tools that got my grandson through Calc I and Calc II. I don't know what he is using for Calc III but they will be using MATLAB for Differential Equations in the Fall. I would have loved to have had a tool like that when I took the subject.
Khan Academy is a great help with all kinds of math. They even have a dedicated EE track. This site is just great!
Now, if you want to learn math and you don't mind spending a bit of money for 'tuition', CalcWorkshop.com is excellent! You can learn at your own pace, of course, but the curriculum is expansive. I have had a subscription (for my grandson) for a couple of years and will maintain it as long as necessary. It's cheap in the bigger scheme of things!
https://calcworkshop.com/courses/It may, or may not, be necessary to start with Algebra but I guarantee that it is PreCalc that sinks students who attempt Calc I without doing it first. Here is where you'll learn trig and all the other tools it takes to succeed in Calculus and beyond.
None of us learned this stuff without a lot of sweat and tears. It takes time, a lot of time!