7+14+21+28+...+105=1*7+2*7+3*7+4*7+...+15*7
15
∑7*n=7*1+7*2+7*3+7*4+...+15*7=7+14+21+28+...+105
n=1
Focus has coordinates (0, a)
a = -3
Thus, 4a = 4(-3) = -12
Because a is negative, we know it will be a concave down or concave left parabola. Hence, A and D can be eliminated. And we know it has to be B because the directrix is the horizontal line y = 3. Hence, the equation of the parabola becomes:

or
Answers:
- x = 4
- AB = 36
- BC = 36
- AC = 36
All three sides are 36 units long.
===========================================================
Explanation:
Triangle ABC is equilateral, so all three sides are the same length.
Pick any two of those sides, set them equal to each other, and solve for x
AB = BC
8x+4 = 11x-8
8x-11x = -8-4
-3x = -12
x = -12/(-3)
x = 4
Use this x value to find each side. We should get the same value (if not, then an error occurred in solving for x).
- AB = 8x+4 = 8*4+4 = 32+4 = 36
- BC = 11x-8 = 11*4-8 = 44-8 = 36
- AC = 9x = 9*4 = 36
We get the same value for the three side lengths, so this confirms we have the correct x value.
Answer:
Option D. 8 units
Step-by-step explanation:
step 1
Find the area of rectangle
The area of rectangle is

step 2
Find the length side of the square with the same area of rectangle
The area of a square is

where
b is the length side of the square
we have

substitute

take the square root both sides

therefore
The length side of the square is 8 units