### Home > GB8I > Chapter 6 Unit 7 > Lesson INT1: 6.4.2 > Problem6-139

6-139.

Plot $ΔMJN$ on graph paper with points $M(3, 3)$, $J(1, 1)$, and $N(6, 1)$.

1. Rotate the triangle $90º$ counterclockwise ($↺$) about the origin. Name the coordinates of the vertices of $ΔM^\prime J^\prime N^\prime$.

Use the eTool to complete the transformation. Notice how the points have changed. Pay attention closely to point $N$.
Notice that the $y$-coordinate has been multiplied by $−1$ and the $x$- and $y$-coordinates are interchanged.

2. Next, reflect $ΔM^\prime J^\prime N^\prime$ across the $y$-axis. Name the coordinates of the vertices of  $\triangle M^{\prime \prime}J^{\prime \prime}N^{\prime \prime}$.

Use the eTool. Notice how the coordinates compare to the coordinates of $\triangle M^{\prime \prime}J^{\prime \prime}N^{\prime \prime}$. What happens to the points when you reflect across the $y$-axis?

$M''(3, 3)$, $J''(1, 1)$, $N''(1, 6)$

3. What is the area of $ΔMJN$?

What is the length of the base, $\overline{JN}$? What is the height from point $M$ to base $\overline{JN}$? Use the area formula for triangles.

Use the eTool below to solve the problem.
Click the link at right for the full version of the eTool: 6-139 HW eTool