12. REINFORCE Consider each reflection be located? a. A triangle in quadrant I, reflected across the \( y \)-axis

When a triangle located in quadrant I is reflected across the \( y \)-axis, the coordinates of each vertex of the triangle will change. In quadrant I, the coordinates of points are positive, meaning they have the form \( (x, y) \) where both \( x \) and \( y \) are greater than 0. When reflecting across the \( y \)-axis, the \( x \)-coordinate of each point changes sign, while the \( y \)-coordinate remains the same. Therefore, if a vertex of the triangle has coordinates \( (x, y) \), after reflection across the \( y \)-axis, its new coordinates will be \( (-x, y) \). As a result, the entire triangle will be located in quadrant II after the reflection, where the \( x \)-coordinates are negative and the \( y \)-coordinates remain positive. In summary, a triangle in quadrant I, when reflected across the \( y \)-axis, will be located in quadrant II.