Porisma

Worked solution

Track five labelled points through eight transformations

The graph of y=f(x)y=f(x) is shown, with A(−1,0)A(-1,0), B(−0.549,−0.631)B(-0.549,-0.631), C(0,0)C(0,0), D(1.215,2.113)D(1.215,2.113) and E(2,0)E(2,0). On separate diagrams, sketch (a) y=f(x−2)y=f(x-2), (b) y=f(−x)+1y=f(-x)+1, (c) y=f(2x+1)y=f(2x+1), (d) y=2f(∣x∣)y=2f(|x|), (e) y=f(−∣x∣)y=f(-|x|), (f) y=∣f(x−2)∣y=|f(x-2)|, (g) y=f(∣x−2∣)y=f(|x-2|), (h) y=1/f(x)y=1/f(x). Indicate clearly, if possible, all coordinates of points corresponding to A, B, C, D and E.

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Given cubic-like graph with A(−1,0), B(−0.549,−0.631) local minimum, C(0,0), D(1.215,2.113) local maximum and E(2,0). Left tail rises and right tail falls. B/D are printed approximate data; no unique formula supplied.
Given cubic-like graph with A(−1,0), B(−0.549,−0.631) local minimum, C(0,0), D(1.215,2.113) local maximum and E(2,0). Left tail rises and right tail falls. B/D are printed approximate data; no unique formula supplied.
Given cubic-like graph with A(−1,0), B(−0.549,−0.631) local minimum, C(0,0), D(1.215,2.113) local maximum and E(2,0). Left tail rises and right tail falls. B/D are printed approximate data; no unique formula supplied.

CJC · Transformations · Example 19

(a) Translate the whole graph right two

Answer

A′(1,0)A\prime(1,0), B′(1.451,−0.631)B\prime(1.451,-0.631), C′(2,0)C\prime(2,0), D′(3.215,2.113)D\prime(3.215,2.113), E′(4,0)E\prime(4,0).

The Teacher asks that composite transformations and replacements be emphasised. Here replace x by x−2x-2: (p,q)↦(p+2,q)(p,q)\mapsto(p+2,q). The source gives the entire first transformed graph. All later coordinate calculations use the printed rounded B/D data consistently; they do not assert more precision for the underlying curve.

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Part (a): separate right-shifted cubic-like sketch f(x−2), with all A′–E′ coordinate labels retained in the text/legend.
Part (a): separate right-shifted cubic-like sketch f(x−2), with all A′–E′ coordinate labels retained in the text/legend.
Part (a): separate right-shifted cubic-like sketch f(x−2), with all A′–E′ coordinate labels retained in the text/legend.
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(b) Reflect, then translate up one

Answer

A′′(1,1)A\prime\prime(1,1), B′′(0.549,0.369)B\prime\prime(0.549,0.369), C′′(0,1)C\prime\prime(0,1), D′′(−1.215,3.113)D\prime\prime(-1.215,3.113), E′′(−2,1)E\prime\prime(-2,1).

Replace x by −x-x to get y=f(−x)y=f(-x), then y by y−1y-1 to get y=f(−x)+1y=f(-x)+1. Intermediate points are A′(1,0)A\prime(1,0), B′(0.549,−0.631)B\prime(0.549,-0.631), C′(0,0)C\prime(0,0), D′(−1.215,2.113)D\prime(-1.215,2.113), E′(−2,0)E\prime(-2,0). The overall map is (p,q)↦(−p,q+1)(p,q)\mapsto(-p,q+1). Both originals print B′′(0.5,0.369)B\prime\prime(0.5,0.369); the x-coordinate must be 0.549 from the given B. Preserve that source typo in native/review evidence; the answer and reconstructed graph use 0.549.

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Part (b): intermediate f(−x), followed by f(−x)+1. Every source intermediate and final point preserved in legends; final B″ x-coordinate corrected from printed 0.5 to 0.549.
Part (b): intermediate f(−x), followed by f(−x)+1. Every source intermediate and final point preserved in legends; final B″ x-coordinate corrected from printed 0.5 to 0.549.
Part (b): intermediate f(−x), followed by f(−x)+1. Every source intermediate and final point preserved in legends; final B″ x-coordinate corrected from printed 0.5 to 0.549.
How did this part go?

(c) Translate left, then halve horizontal distances

Answer

A′′(−1,0)A\prime\prime(-1,0), B′′(−0.7745,−0.631)B\prime\prime(-0.7745,-0.631), C′′(−0.5,0)C\prime\prime(-0.5,0), D′′(0.1075,2.113)D\prime\prime(0.1075,2.113), E′′(0.5,0)E\prime\prime(0.5,0).

Translate left 1, obtaining y=f(x+1)y=f(x+1); then replace x by 2x2x to obtain y=f(2x+1)y=f(2x+1). The intermediate points are A′(−2,0)A\prime(-2,0), B′(−1.549,−0.631)B\prime(-1.549,-0.631), C′(−1,0)C\prime(-1,0), D′(0.215,2.113)D\prime(0.215,2.113), E′(1,0)E\prime(1,0). The overall map is (p,q)↦((p−1)/2,q)(p,q)\mapsto((p-1)/2,q). The Teacher says this repeats Example 8 and need not be treated in detail again; reuse that replacement method while preserving both source diagrams and every coordinate here.

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Part (c): f(x+1) and f(2x+1), including all translated and horizontally halved coordinate labels. Source A′/C′ prime-count inconsistencies do not alter the corresponding points.
Part (c): f(x+1) and f(2x+1), including all translated and horizontally halved coordinate labels. Source A′/C′ prime-count inconsistencies do not alter the corresponding points.
Part (c): f(x+1) and f(2x+1), including all translated and horizontally halved coordinate labels. Source A′/C′ prime-count inconsistencies do not alter the corresponding points.
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(d) Mirror the right side, then double outputs

Answer

C gives (0,0)(0,0); D gives (±1.215,4.226)(\pm1.215,4.226); E gives (±2,0)(\pm2,0). A and B are discarded.

First retain original inputs p≥0p\ge0 and reflect them to form y=f(∣x∣)y=f(|x|). The intermediate D images are (±1.215,2.113)(\pm1.215,2.113) and E images (±2,0)(\pm2,0), with C unchanged. Then replace y by y/2y/2: y/2=f(∣x∣)y/2=f(|x|), hence y=2f(∣x∣)y=2f(|x|). The source final plot has doubled heights 4.226 but is mislabelled y=f(∣x∣)y=f(|x|); preserve that typo in native/review text and label the actual final graph with its factor 2. Negative-input A/B are not carried into this construction.

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Part (d): intermediate f(|x|), then final 2f(|x|). C remains origin; D has mirrored heights 2.113 then 4.226; E remains at ±2. A/B are discarded. Final equation label includes the source-omitted factor 2.
Part (d): intermediate f(|x|), then final 2f(|x|). C remains origin; D has mirrored heights 2.113 then 4.226; E remains at ±2. A/B are discarded. Final equation label includes the source-omitted factor 2.
Part (d): intermediate f(|x|), then final 2f(|x|). C remains origin; D has mirrored heights 2.113 then 4.226; E remains at ±2. A/B are discarded. Final equation label includes the source-omitted factor 2.
How did this part go?

(e) Keep and mirror the original left side

Answer

A gives (±1,0)(\pm1,0); B gives (±0.549,−0.631)(\pm0.549,-0.631); C gives (0,0)(0,0). D and E are discarded.

First reflect in the y-axis to obtain y=f(−x)y=f(-x), with intermediate A′(1,0), B′(0.549,−0.631), C′(0,0), D′(−1.215,2.113), E′(−2,0). Retain the right-hand half of this reflected graph and mirror it to obtain y=f(−∣x∣)y=f(-|x|). Equivalently, retain original inputs p≤0p\le0, then duplicate them symmetrically. The displayed intermediate and final source sketches are both retained.

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Part (e): f(−x), then f(−|x|), with the original left half duplicated. A at ±1, B at ±0.549 with height −0.631 and C at 0 survive; original D/E are discarded.
Part (e): f(−x), then f(−|x|), with the original left half duplicated. A at ±1, B at ±0.549 with height −0.631 and C at 0 survive; original D/E are discarded.
Part (e): f(−x), then f(−|x|), with the original left half duplicated. A at ±1, B at ±0.549 with height −0.631 and C at 0 survive; original D/E are discarded.
How did this part go?

(f) Translate before taking output modulus

Answer

A gives (1,0)(1,0), B gives (1.451,0.631)(1.451,0.631), C gives (2,0)(2,0), D gives (3.215,2.113)(3.215,2.113), E gives (4,0)(4,0).

Translate right 2 to obtain y=f(x−2)y=f(x-2); the intermediate coordinates are exactly those in part (a). Then reflect only the negative-output arcs in the x-axis, giving y=∣f(x−2)∣y=|f(x-2)|. The map is (p,q)↦(p+2,∣q∣)(p,q)\mapsto(p+2,|q|). B changes output sign; A/C/E stay on the axis and D stays above it. Both source stages and all coordinates are retained.

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Part (f): intermediate shifted graph f(x−2), then |f(x−2)|. B moves from height −0.631 to 0.631, with all other labelled output heights unchanged.
Part (f): intermediate shifted graph f(x−2), then |f(x−2)|. B moves from height −0.631 to 0.631, with all other labelled output heights unchanged.
Part (f): intermediate shifted graph f(x−2), then |f(x−2)|. B moves from height −0.631 to 0.631, with all other labelled output heights unchanged.
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(g) Translate the input-modulus graph right two

Answer

C gives (2,0)(2,0); D gives (0.785,2.113)(0.785,2.113) and (3.215,2.113)(3.215,2.113); E gives (0,0)(0,0) and (4,0)(4,0). A and B are discarded.

First retain the original p≥0p\ge0 side and mirror it: y=f(∣x∣)y=f(|x|) has C(0,0), D-images (±1.215,2.113)(\pm1.215,2.113) and E-images (±2,0)(\pm2,0). Then replace x by x−2x-2 to obtain y=f(∣x−2∣)y=f(|x-2|), symmetric about x=2x=2. For each retained input p, the two images have x-coordinates 2±p2\pm p. At p0 the two images coincide, so C is counted once. This differs from taking output modulus in part (f).

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Part (g): intermediate f(|x|), then f(|x−2|), whose symmetry axis is x=2. D at 0.785 and 3.215, E at 0 and 4, C at 2; original A/B discarded.
Part (g): intermediate f(|x|), then f(|x−2|), whose symmetry axis is x=2. D at 0.785 and 3.215, E at 0 and 4, C at 2; original A/B discarded.
Part (g): intermediate f(|x|), then f(|x−2|), whose symmetry axis is x=2. D at 0.785 and 3.215, E at 0 and 4, C at 2; original A/B discarded.
How did this part go?

(h) Reciprocate non-zero outputs

Answer

B′≈(−0.549,−1.585)B\prime\approx(-0.549,-1.585), D′≈(1.215,0.473)D\prime\approx(1.215,0.473); vertical asymptotes x=−1,0,2x=-1,0,2 and horizontal asymptote y=0y=0.

A, C and E have zero outputs, so they have no finite reciprocal images and their x-coordinates become poles in the supplied continuous sketch. From the printed rounded data, 1/(−0.631)≈−1.5851/(-0.631)\approx-1.585 and 1/2.113≈0.4731/2.113\approx0.473. B becomes a local maximum and D a local minimum. Preserve all four reciprocal branches and the original unbounded tail behaviour, giving horizontal limit 0. The reciprocal is undefined at 0, so it has no y-intercept; it has no x-intercept either. The source repeats the original given diagram beside this reciprocal, and both are retained.

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Part (h): original labelled cubic-like graph and its four-branch reciprocal. Poles −1,0,2; horizontal 0; B′ approximately (−0.549,−1.585), D′ approximately (1.215,0.473). No finite images of A,C,E.
Part (h): original labelled cubic-like graph and its four-branch reciprocal. Poles −1,0,2; horizontal 0; B′ approximately (−0.549,−1.585), D′ approximately (1.215,0.473). No finite images of A,C,E.
Part (h): original labelled cubic-like graph and its four-branch reciprocal. Poles −1,0,2; horizontal 0; B′ approximately (−0.549,−1.585), D′ approximately (1.215,0.473). No finite images of A,C,E.
How did this part go?