Question

Please help me and show work on a piece of paper​

Answer 1

Let's start with proving that side AB is parallel to side CD

First off, let's find the slope of line AB. So we'll use the slope formula.

$A = (x_1,y_1) = (2,-1)\\\\B = (x_2,y_2) = (1,3)\\\\m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}\\\\m = \frac{3 - (-1)}{1 - 2}\\\\m = \frac{3 + 1}{1 - 2}\\\\m = \frac{4}{-1}\\\\m = -4$

The slope of AB is -4.

Now let's find the slope of line CD.

$C = (x_1,y_1) = (6,5)\\\\D = (x_2,y_2) = (7,1)\\\\m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}\\\\m = \frac{1 - 5}{7 - 6}\\\\m = \frac{-4}{1}\\\\m = -4$

The slope of CD is also -4.

Recall that parallel lines always have equal slope (but different y intercepts).

This proves that AB is parallel to CD.

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We'll follow the same steps to show that AD is parallel to BC.

Find the slope of AD

$A = (x_1,y_1) = (2,-1)\\\\D = (x_2,y_2) = (7,1)\\\\m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}\\\\m = \frac{1 - (-1)}{7 - 2}\\\\m = \frac{1 + 1}{7 - 2}\\\\m = \frac{2}{5}$

Now find the slope of BC

$B = (x_1,y_1) = (1,3)\\\\C = (x_2,y_2) = (6,5)\\\\m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}\\\\m = \frac{5 - 3}{6 - 1}\\\\m = \frac{2}{5}$

We get 2/5 each time, so these lines are parallel as well.

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In short, the first section shows that AB is parallel to CD. The second section proved that AD is parallel to BC.

Because we have two pairs of parallel opposite sides, we can say that ABCD is a parallelogram.

Edit: I have attached the diagram below.