sinx = -2/(5^0.5)
3pi/2 < x < 2pi
the question that i donīt understand is that i shuold use this values and decide the exacly value of this expression: cos(2x-3pi/4)
so i did this way
arcsin(-2/(5^0.5) = x = -63.4
cos(2*(-63.4)-3pi/4)
are i doing right ?
Not quite!
You are being asked to calculate an exact value, so you need to proceed
similarly to Prove It's method.
You could reference the Unit Circle also and write
Also, the angle x is in the 4th quadrant from the range of x given.
You could sketch a right-angled triangle and use Pythagoras' theorem to find
Therefore....
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