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Worked solution

Account for order in two vertical transformations

State a sequence of transformations which transforms the graph of y=f(x)y=f(x) to the graph of y=2f(x)+1y=2f(x)+1.

CJC · Transformations · Example 9

Method 1: scale, then translate

Answer

Scale parallel to the y-axis by factor 2, then translate 1 unit in the positive y-direction.

The Teacher emphasises y replaced by y/2y/2, followed by y replaced by y−1y-1. The source recommends scaling before translation for vertical changes.

Double output distances

y2=f(x)⟹y=2f(x)\frac y2=f(x)\quad\Longrightarrow\quad y=2f(x)

Replace y by y/2y/2 and solve for y.

Translate up one unit

y−1=2f(x)⟹y=2f(x)+1y-1=2f(x)\quad\Longrightarrow\quad y=2f(x)+1

Apply the y-replacement to the current equation.

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Method 2: translate, then scale

Answer

Translate 1/21/2 unit in the positive y-direction, then scale parallel to the y-axis by factor 2.

The Teacher emphasises y replaced by y−1/2y-1/2, followed by y replaced by y/2y/2. The later scaling also doubles the earlier translation.

Translate up one half

y−12=f(x)⟹y=f(x)+12y-\frac12=f(x)\quad\Longrightarrow\quad y=f(x)+\frac12

Use the smaller translation before doubling.

Double all outputs

y2=f(x)+12⟹y=2f(x)+1\frac y2=f(x)+\frac12\quad\Longrightarrow\quad y=2f(x)+1

The constant term is doubled as well.

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