<h2>
Explanation:</h2>
In every rectangle, the two diagonals have the same length. If a quadrilateral's diagonals have the same length, that doesn't mean it has to be a rectangle, but if a parallelogram's diagonals have the same length, then it's definitely a rectangle.
So first of all, let's prove this is a parallelogram. The basic definition of a parallelogram is that it is a quadrilateral where both pairs of opposite sides are parallel.
So let's name the vertices as:

First pair of opposite sides:
<u>Slope:</u>

Second pair of opposite sides:
<u>Slope:</u>

So in fact this is a parallelogram. The other thing we need to prove is that the diagonals measure the same. Using distance formula:

So the diagonals measure the same, therefore this is a rectangle.
Answer: C
Step-by-step explanation:
We know that
, and thus by the exterior angle theorem,

Thus, 
Answer:
0.75c
Step-by-step explanation:
If we have an expression as:
a*x + b*x
We can see that both terms in the expression, a*x and b*x have an x, so we can call the x a common factor and we can write an equivalent expression as:
a*x + b*x = (a + b)*x
If we replace, for example, a by 2, b by 3 and x by 4, we can test the expression as:
2*4 + 3*4 = (2 + 3)*4
8 + 12 = (5)*4
20 = 20
Therefore, if we have the following expression:
c - 0.25*c
The expression that is equivalent is 0.75c and it is calculated as:
c - 0.25*c = (1 - 0.25)*c
c - 0.25*c = 0.75*c
Answer:
32
Step-by-step explanation:
Suppose Alvin is x years old. Then Elga is x+15 years old.
x+x+15=49
2x=34
x=17
17+15=32