To rotate a point counterclockwise about the origin by 90 degrees, you can use the following transformation formula:
If the original point is \((x, y)\), the new coordinates \((x', y')\) after a 90-degree rotation are given by:
\[ (x', y') = (-y, x) \]
For the point \((1, 2)\):
- \(x = 1\)
- \(y = 2\)
Applying the transformation:
\[ x' = -y = -2 \] \[ y' = x = 1 \]
Thus, the new point after rotating \((1, 2)\) 90 degrees counterclockwise about the origin is \((-2, 1)\).