# It is known that the graph of direct proportionality passes through point A (3; 21).

It is known that the graph of direct proportionality passes through point A (3; 21). Does this graph pass through point B (-7; -49); point C (-5; 3.5); point D (0.8; -5 , 6)?

Decision.

y = kx – formula of direct proportionality.

Because the graph passes through point A (3; 21), then the equality is true:

21 = k * 3;

k = 21: 3;

k = 7.

So our function is: y = 7x.

Now let’s check the rest of the points by substituting their coordinates into the formula:

B (-7; -49):

-49 = 7 * (-7)

-49 = -49 – true, so the graph goes through point B.

C (-5; 3.5):

3.5 = 7 * (-5)

3.5 = -35 – incorrect, which means the graph does not pass through point C.

D (0.8; -5.6):

-5.6 = 7 * 0.8

-5.6 = 5.6 – incorrect, so the chart does not pass through point D.

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