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Topic 2.2 ยท Linear Test
How do you identify a LINEAR function from a table?
Equal ฮx intervals
Think: what stays constant?
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Topic 2.2 ยท Exponential Test
How do you identify an EXPONENTIAL function from a table?
Equal ฮx intervals
Think: what stays constant?
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Topic 2.2 ยท Key Distinction
How does a linear function change vs. an exponential function?
Linear: f(x) = b + mx
Expo: f(x) = aยทbหฃ
Addition vs multiplication
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Topic 2.2 ยท Sequences โ Functions
Arithmetic sequence โ which function type? Geometric sequence โ which function type?
Both have parallel formulas
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Topic 2.2 ยท Point-Slope โ Linear
Write the point-slope form for an arithmetic sequence / linear function given a known point (k, aโ).
Like slope-intercept but anchored at k
6/10
Topic 2.2 ยท Point-Slope โ Exponential
Write the point-slope form for a geometric sequence / exponential function given a known point (k, aโ).
Like standard form but anchored at k
7/10
Topic 2.2 ยท Finding r (Example 2)
P(3)=43 and P(6)=140 model a geometric sequence. Write the equation for r.
P(n) = 43ยทr^(nโ3)
Substitute n=6, then solve for r
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Topic 2.2 ยท Finding m (Example 3)
Theater: row 5 has 31 seats, row 11 has 49 seats. Find the common difference m.
s(n) = 31 + mยท(nโ5)
Substitute n=11, solve for m
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โ Exponential Test
Constant RATIO between outputs
Divide consecutive outputs. If ratio is always the same โ Exponential.
Change is based on multiplication.
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โ Linear Test
Constant DIFFERENCE between outputs
Subtract consecutive outputs. If difference is always the same โ Linear.
Change is based on addition.
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โ Sequences โ Functions
Arithmetic โ Linear ยท Geometric โ Exponential
Arithmetic (add d each term) behaves like linear.
Geometric (multiply by r each term) behaves like exponential.
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โ Key Distinction
Linear: add same amount ยท Exponential: multiply same ratio
Linear: change d based on addition โ constant rate.
Exponential: change r based on multiplication โ proportional change.
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โ Point-Slope โ Exponential
aโ = aโ ยท r^(n โ k)
Anchor at your known point (k, aโ). The exponent is (nโk) โ the number of steps from k.
Equivalent: f(x) = f(xโ)ยทb^(xโxโ)
5/10
โ Point-Slope โ Linear
aโ = aโ + dยท(n โ k)
Anchor at your known point (k, aโ). Add d for each step away from k.
Equivalent: f(x) = f(xโ) + mยท(xโxโ)
8/10
โ Common Difference m
m = 3
s(11) = 31 + mยท(6) = 49 โ 6m = 18 โ m = 3.
s(25) = 31 + 3ยท(20) = 91 seats.
7/10
โ Finding r (Example 2)
r = (140/43)^(1/3)
43ยทrยณ = 140 โ rยณ = 140/43 โ r = (140/43)^(1/3).
Cube root because the span is 3 days (6โ3=3).
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Topic 2.2 ยท Neither
g(x): outputs 0, 1, 4, 9, 16 over equal intervals. Is it linear, exponential, or neither? Why?
Check differences then ratios
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Topic 2.2 ยท Two-Point Rule
If you are given any two points of a function, what can you always write?
Four possible answers
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โ Two-Point Rule
Linear, exponential, arithmetic, or geometric
Two points are always enough to write a linear function, exponential function, arithmetic sequence, or geometric sequence using point-slope form.
9/10
โ Neither
Neither โ differences AND ratios are not constant
Differences: 1, 3, 5, 7 โ not constant โ not linear.
Ratios: undef, 4, 9/4... โ not constant โ not exponential.
โ Neither.