1) start with (x-h)^2 + (y-k)^2 = r^2. Insert the given info: center at (-1,8) and radius 5:
(x+1)^2 + (y-8)^2 = 5^2 (answer)
The new parking lot must hold twice as many cars as the previous parking lot. The previous parking lot could hold 56 cars. So this means the new parking lot must hold 2 x 56 = 112 cars
Let y represent the number of cars in each row, and x be the number of total rows in the parking lot. Since the number of cars in each row must be 6 less than the number of rows, we can write the equation as:
y = x - 6 (1)
The product of cars in each row and the number of rows will give the total number of cars. So we can write the equation as:
xy = 112 (2)
Using the above two equations, the civil engineer can find the number of rows he should include in the new parking lot.
Using the value of y from equation 1 to 2, we get:
x(x - 6) = 112 (3)
This equation is only in terms of x, i.e. the number of rows and can be directly solved to find the number of rows that must in new parking lot.
For example:
x+2y=7
6x+7y=2
__________
x=7-2y *
6*(7-2y)+7y=2 **
__________
x=7-2y
42-12y+7y=2
__________
x=7-2y
-5y=-40
__________
x=7-2y
y=8
x=-9
This problem can be readily solved if we are familiar with the point-slope form of straight lines:
y-y0=m(x-x0) ...................................(1)
where
m=slope of line
(x0,y0) is a point through which the line passes.
We know that the line passes through A(3,-6), B(1,2)
All options have a slope of -4, so that should not be a problem. In fact, if we check the slope=(yb-ya)/(xb-xa), we do find that the slope m=-4.
So we can check which line passes through which point:
a. y+6=-4(x-3)
Rearrange to the form of equation (1) above,
y-(-6)=-4(x-3) means that line passes through A(3,-6) => ok
b. y-1=-4(x-2) means line passes through (2,1), which is neither A nor B
****** this equation is not the line passing through A & B *****
c. y=-4x+6 subtract 2 from both sides (to make the y-coordinate 2)
y-2 = -4x+4, rearrange
y-2 = -4(x-1)
which means that it passes through B(1,2), so ok
d. y-2=-4(x-1)
this is the same as the previous equation, so it passes through B(1,2),
this equation is ok.
Answer: the equation y-1=-4(x-2) does NOT pass through both A and B.
