Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

To 2 decimal places, what is the value of the lower-right entry in the reflection matrix $Q_a $if a = 1.05?

Not even sure where to begin, is there a formula?

This is what I could find in my textbook enter image description here

share|cite|improve this question
"in the reflection matrix $Q_a$" - what is the definition of $Q_a$ ? – Belgi Oct 21 '12 at 15:37
Thats it the question I was given. – JackyBoi Oct 21 '12 at 15:45
@Belgi this has to do with transformations – JackyBoi Oct 21 '12 at 15:46
There is no universal definition of $Q_a$. You're going to have consult your textbook, class notes, or your instructor to determine the meaning of this symbol before proceeding. – Michael Joyce Oct 21 '12 at 16:02
@MichaelJoyce I have edited my question please take a look. – JackyBoi Oct 22 '12 at 1:25

Okay, well the lower right entry of the matrix $q_a$ is $-\cos(2a)$. So plug in $a = 1.05$ and use a calculator to get an approximate value for $-\cos(2.10) \approx 0.50485$. Be sure to use 'radian' mode on your calculator. (Always assume angle measures for trigonometric functions are in radians unless explicitly told otherwise.)

share|cite|improve this answer
thats exactly what I was thinking as well.. but with one exception that I did not use radian mode I will do that now – JackyBoi Oct 22 '12 at 2:25

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.