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Which of the following equations is an example of direct variation?

y + 10 = 2(x + 5)
y = 2(x + 5)
y + 5 = 2(x + 5)
y = x + 5

Please help!



Answer :

Direct variation is when  x/y = constans 
That's mean, that   formula of direct variation is y=kx   (k inequal 0)

First:
y+10=2(x+5)
y+10 = 2*x + 2*5
y+10=2x+10     /subtract 10 
y=2x  
It is  y=kx.  Here  k=2   -  it is example of direct variation.

Next:
y=2(x+5)
y=2*x + 2*5
y=2x+10
It is not  y=kx  (because you've got +10). So it isn't. 

Next:
y+5=2(x+5)
y+5=2x+10   /subtract 5
y=2x+5
It isn;t too, because you've got  +5.

Next:
y=x+5   isn't, because you've got +5. 

So only first equation

Answer:

y + 10 = 2(x + 5)

Step-by-step explanation:

Direct variation is a mathematical relationship between any two variables which can be expressed by equation in which one of the variable is equal to a constant times of the other variable.

So, y  = kx

where k is any number.

Considering A as:

y + 10 = 2(x + 5)

Solving,

y = 2x ,  this is a direct variation.

Considering B as:

y = 2(x + 5)

Solving,

y = 2x + 10,  this is not a direct variation.

Considering C as:

y + 5 = 2(x + 5)

Solving,

y = 2x + 5,  this is not a direct variation.

Considering D as:

y = x + 5, this is not a direct variation.

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