MHB Apc.trig.08 quantity choice on y value

[karush]

The line containing point A is rotated $90^o$ anticlockwise about the origin O

$\begin{array}{ll}
\textit{The y coordinate of point A }
& \textit{The y coordinate point A}\\
\textit{before rotation}
& \textit{After rotation}
\end{array}$
a. The quantity on the left is greater
b. The quantity on the right is greater
c. Both are equal
d. The relationship cannot be determined without furthor information

well this seems very easy but many have missed it

rotating it into the 4th quadrant will makes the signs of (x,y) to be (+,-) Thus a.

however the x coordinate would be equal...

 

[skeeter]

let $r$ be the distance from the origin to A

x-coordinate changes sign from + to -

$r\cos(135) = -r\cos(45)$

y-coordinate stays the same

$r\sin(135) = r\sin(45)$

 

[karush]

let $r$ be the distance from the origin to A

x-coordinate changes sign from + to -

$r\cos(135) = -r\cos(45)$

y-coordinate stays the same

$r\sin(135) = r\sin(45)$

so quantity means distance not sign

 

[skeeter]

(0,-5) and (0,5) are the same distance from the x-axis, but the positive y-coordinate is the greater quantity …

5 > -5

 

[karush]

I think it is confusing exactly what they are asking

 

[skeeter]

both y-coordinates are the same

how is that confusing?

 

[karush]

one y=5 the other y=-5

 

[skeeter]

one y=5 the other y=-5

no … both are positive in your original posted problem

y-values in quadrants I and II are > 0

 

[karush]

I confess I rotated it into the 4thQ not 2ndQ

 

[skeeter]

I confess I rotated it into the 4thQ not 2ndQ

… it happens.

 

[HOI]

Look at a clock! Or does everyone have digital clocks now and don't know what "clockwise" and "anti-clockwise" mean? (Though I would say "clockwise" and "counter-clockwise".)

 

[karush]

yeah just spaced on it
circular clocks are what cave men had

 

[HOI]

Oh, God! I feel so old!

 

[karush]

well you know more than me and I'm 76

 

[HOI]

Okay, so you are younger than I am- don't rub it in!

 

[topsquark]

Look at a clock! Or does everyone have digital clocks now and don't know what "clockwise" and "anti-clockwise" mean? (Though I would say "clockwise" and "counter-clockwise".)

Deosil and widdershins.

-Dan

 

[karush]

so far it been a lot of work but almost 50,000 views on the problems

https://dl.orangedox.com/6rStfn4eMFHuHvAKuX