Radians??????

[RM2020]

1,
A current waveform may be described by… is = 13 cos (2πft − π/ 4 ) [A] where frequency, f = 1Hz and t represents time. Make time (t) the subject of this formula and hence determine a point in time when the current waveform has a magnitude of +10A

2,
The instantaneous value of a power signal may be described by; 12∠ ( 3π/ 8 ) [W] Find the magnitude of the vertical and horizontal components of this signal. Note that the symbol ∠ indicates ‘angle’.

PLEASE HELP WAY ITS OVER MY HEAD

 

[Dr.Peterson]

I presume that's supposed to be I = 13 cos(2πft − π/4), yielding a current in amperes. Replacing f with its value, 1, you have I = 13 cos(2πt − π/4).

To solve for t, divide both sides by 13, then take the inverse cosine of both sides, and proceed to isolate t. (This will, of course, only give you one of infinite times when the current has a given value.) Then plug in 10 for I to answer the question, evaluating with a calculator.

For the second problem, please tell us what you have learned about the notation used here, called phasor notation or polar form. Here is one source for information about it.