Which of these in an equivalent trigonometric expression for sinx:

A. -cos(pi/2 - x)
B. sin(pi/2 -x)
C. cos (x + pi/2)
D. -cos(x +pi/2)

Please also explain why and how you picked it!

Question

Which of these in an equivalent trigonometric expression for sinx:

A. -cos(pi/2 - x)
B. sin(pi/2 -x)
C. cos (x + pi/2)
D. -cos(x +pi/2)

Please also explain why and how you picked it!

anonymous · Answer

...?

anonymous · Answer

post the freaking link plz

anonymous · Answer

can someone just answer my question???

ghazi · Answer

why you guys are doing this sin x = cos (90-x)

anonymous · Answer

Please?

anonymous · Answer

@ghazi I don't know It's a question in my Advanced Function Textbook...

anonymous · Answer

Christians4 your thread has been a little hijacked. To help (then you can close it), It is C. Draw a sinx graph and a cosx graph. They are the same if you 'slide' the cosx graph along by 90 degrees (pi/2) to the right (+ direction). so sinx = cos(x + pi/2)!

anonymous · Answer

Thanks but I don't know how to draw the graph on top of my head and cant use a graphing calculator, Is there a way to do it another way? equation wise or something?

anonymous · Answer

|dw:1352387129391:dw|
see now? the cosx is the dotted line (sorry about the scale!) slide it along 90 degrees, it matches up!