Question

Why is my T-84 plus calculator showing "Err:Dom", when i plug in 1/(tan pi/2) (which is the same as cot(pi/2), which should be 0) ?

Answer 1

Because the tangent of pi/2 is undefined.

Answer 2

because tan(x)-> infinity as x -> pi/2

the calculator just complains....

Answer 3

The tangent is sin/cos
The cos of pi/2 is 0 so that denominator is 0 and thus the fraction is undefined.

Answer 4

no such thing as tan90

Answer 5

If you are flying at a 90 degree angle..how far must you travel until you cover 2000 feet ground distance (no wind)..............

Answer 6

I have always thought cot pi/2 is 0, so that is undefined too?

Answer 7

http://www.regentsprep.org/Regents/math/algtrig/ATT7/othergraphs.htm, according to this, cot pi/2 is 0.

Answer 8

yes cot pi/2 = 0

use Mertz's idea

cot x= cos(x)/sin(x)

Answer 9

Alright, but then why does it show up as domain error on my ti84?

Answer 10

I don't know...I don't have a cot function on my calculator.

Answer 11

I used 1/tan instead of cot since it wasn't on my calculator too, and it was showing that error :(.

Answer 12

The calculator does exactly what you asked it to do: evaluate tan(pi/2) and then take the reciprocal. It cannot complete the first step, so it breaks.
If you know the simplification, give it the simplified version.

Answer 13

Alright I see what you mean, I typed it in like this 1/tan(pi/2), so how should I change it so it works?

Answer 14

Knowing that tan(pi/2)=inf, then you would replace cot(pi/2) with zero in your expression to avoid the problem.

Answer 15

Sorry, I'm not understanding, what should I type in again?

Answer 16

you should just recognize that 1/tan(pi/2) is undefined and cot (pi/2) is zero

however, if you insist on using a calculator to find the value of cot(pi/2), type in cos(pi/2)/sin(pi/2)
this uses the identity cot(x) = cos(x)/sin(x)