2y=5x+1Not a direct variationDirect variation, constant of variation is -Direct variation, constant of variation isDirect variation, constant of variation is 1--
Accepted Solution
A:
Answer:Step-by-step explanation:he whole assignment seems to deal only with one simple concept, a direct variation
Sometimes text or your notes have definitions that are difficult to understand.
Here is the definition that is easy to understand:
A direct variation gives you an equation that contains no constants, and there are no exponents on the two variables.
e.g. y = 8x is a direct variation,
but y = 8x + 4 is NOT, since I see a constant of 4
a direct variation can be written in the form
y = kx , where k is the constant of variation
#1, not a variation, I see a +1 sitting there as a constant
#2, yes it is a direct variation:
-12x = 6y
6y = -12x
y = -2x
so the constant of variation is -2 , if y varies directly with x
or
-12x = 6y
x = -(1/2)x
now the constant of variation is -1/2 , if x varies directly as y
so it depends how you express the equation, either in terms of x or in terms of y
#3,
.7x - 1.4y = 0
.7x = 1.4y
1.4y = .7x
y = (.7/1.4)x = (1/2)x
so , yes it is, and the constant of variation is 1/2
From #4 on, you have to first find the equation.
I will do #4, you try the remaining.
#4, they tell us it is a direct variation, so it must look like
y = kx
They give us x=2 when y = -10
let's plug in those values:
-10 = k(2)
2k = -10
k = -5
aaahhhh, so y = -5x is our equation
#6, same way, just some fractions to deal with
#7, to graph, pick any x, and find the y to get ordered pairs,
e.g. let x = 3, then y = (1/3)(3) = 1, --> point(3,1)
let x = 9, then y = (1/3)(9) = 3 ---> point (9,3)
plot those two points, and join with a straight line
Notice how I picked multiple of 3's for my x's so I could take 1/3 of the x without ending up with fractions?
#8 , same as #7, pick multiples of 2 for your x's
#9 and #10 are the same type
#9
assume it is a direct variation, then its equation must be
y = kx
use the first given data: x = 3, y = 5.4
then 5.4 = k(3)
3k = 4.5
k = 1.5
equation is y = 1.5x
do the other points satisfy our equation?
for (7, 12.6)
is 12.6 = 1.5(7) ?
12.6 = 10.5 ??? NO, so the given data is NOT a direct variation
#10 same way