establishing an identity

alyren said:
Sec[(pi/2) + u]= -csc

how to start this?

Your question does not make any sense tome.

What is the "arguement" of csc?
 
\(\displaystyle sec(\pi/2+u) \ = \ \frac{1}{cos(\pi/2+u)} \ = \ \frac{1}{cos(\pi/2)cos(u)-sin(\pi/2)sin(u)} \ = \ \frac{1}{-sin(u)} \ = \ -csc(u).\)
 
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