Question

Sandra wants to evaluate 2 cot(-9pi/2). Her work is shown below. what did she do wrong?

2 cot (-9pi/2) = 2 cot (9pi/2)
2 cot (-9pi/2) = 2 cot (pi/2)
2 cot (-9pi/2) = 2(0)
2 cot (-9pi/2) = 0


a)Since cot is an odd function 2 cot (-9pi/2) does not equal 2 cot(9pi/2)

b) since cot has a period of (pi) 2 cot(9pi/2) does not equal 2 cot (pi/2)

c) since cot evaluated at pi/2 is not 0, 2 cot(pi/2) does not equal 2(0)

d) since cot cannot be multiplied by a factor 2(0) does not equal 0

Answer 1

Answer:

Option A - Since cot is an odd function  $2 cot(-\frac{9\pi}{2})$ does not equal  $2 cot(\frac{9\pi}{2})$               

Step-by-step explanation:

Given : Sandra wants to evaluate $2 cot(-\frac{9\pi}{2})$

To find : What did she do wrong?

Solution : In the first step she took a wrong step because cot is an odd function so $cot(-x)= -cot x$

The exact steps are :

$2cot(-\frac{9\pi}{2})=-2cot (\frac{9\pi}{2})$

$2cot(-\frac{9\pi}{2})=-2cot (\frac{\pi}{2})$

$2cot(-\frac{9\pi}{2})=-2(0)$

$2cot(-\frac{9\pi}{2})=0$

Therefore, option A is correct .