You are given two points on a line, and told that the function is "direct variation." You can save a lot of time by recognizing that the y-intercept here is zero (0). Thus, the line passes through the origin.
A line through (2,14) and (4,38) is NOT direct variation, because the line connecting those two points does NOT pass through the origin, and thus has a vertical intercept.
X^2 = 16 (after subtracting 9 from both sides)
x = 4
The heights of the tree form an arithmetic sequence. The first measurement is 200 cm, so the first term a₁=200. The tree grows 0.5 cm per week, so the common difference d=0.5.

The equation for the weekly height is:

where n is the number of week.
<span>The line is horizontal. The slope is 0.
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