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# Vertices of a triangle and rotations. watch

1. Ghjng
2. (Original post by Deeboss)
Suppose A(5, 8) is a vertex of a triangle. After the triangle is rotated counter-clockwise
30 degrees around the coordinate origin, the coordinates of vertex A is transformed
from (5, 8) into (x, y). Find coordinate x. (Rounding your answer to 2 decimal places)

I used the following method: -

Rotation of axes Theta: (x.y) ---> (X.Y)

X=xcos(theta)+ysin(theta)
Y=-xsin(theta)+ycos(theta)

In 30 degrees my answer for X to 2.dp is 8.33

Both of these answers were wrong in my coursework and I am not so sure where I went wrong could someone help me out with this please, and show me your method of working, and answer. Also let know if I was on the right track to working this out?
Matrix rotation. You got one of your signs wrong.

X=xcos(theta)-ysin(theta)
Y=xsin(theta)+ycos(theta)
3. (Original post by RDKGames)
Matrix rotation. You got one of your signs wrong.

X=xcos(theta)-ysin(theta)
Y=xsin(theta)+ycos(theta)
So the answer would be 0.33 (2.dp)? Please let me know if this is correct. Aahaha what a small error that could of got me for 5 marks.
4. (Original post by Deeboss)
So the answer would be 0.33 (2.dp)? Please let me know if this is correct. Aahaha what a small error that could of got me for 5 marks.
Yes.

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