C = 2πr
141.3 = 2(3.14)r
141.3 = 6.28r
22.5 = r
The steps involving properties of equality are shown in painful detail.
For Step 4, you add 7 to both sides of the equation (with the goal of cancelling the -7 on the left). So you have
6x -7 +7 = 12 +7 . . . . . . . showing 7 added to both sides
In the next step, this is simplified to the way you might have written it to start with:
6x = 19
There should be no confusion in any of this. All solutions of all equations make use of the properties of equality like this. Addition is used to cancel subtraction, division is used to cancel multiplication. (Root-taking cancels powers, and vice-versa; inverse trig functions cancel trig functions; and so on.)
Jacob wants to build a rectangular enclosure for his animals. One side of the pen will be against the barn,so he needs no fence on that side.
Let w be the width of the enclosure (perpendicular to the barn) and let l be the length of the enclosure (parallel to the barn).
one side of the length is not counted for perimeter because one side of length will be against the barn.
Perimeter = 400 ft
Perimeter of rectangle = L + W + W
400 = L + 2W
L = 400 - 2W
Area = L * W
Replace L by 400 - 2W
A(W) = (400 - 2W) * W

Now we find out x coordinate of vertex to find the width that maximize the area

a= -2 and b = 400

The width w would maximize the area is w = 100ft
To find maximum area we plug in 100 for W in A(W)


the maximum area is 20,000 square feet
Let the number of hour it took them to have completed the same number of problems be x, then
15 + 10x = 9 + 12x
12x - 10x = 15 - 9
2x = 6
x = 6/2 = 3
After 3 hours, they must have completed the same number of homeworks.