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Mathematics Dictionary
Dr. K. G. Shih

Power 5 Equation or quaint equation
Questions


Answers


Q01. Solve x^5 + 1 = 0

De Moivre's Theory : Draw a unit circle
  • 1. Draw 1st point on circle with angle : A1 = 036
  • 2. Draw 2nd point on circle with angle : A2 = 108
  • 3. Draw 3nd point on circle with angle : A3 = 180
  • 4. Draw 4nd point on circle with angle : A3 = 252
  • 5. Draw 5nd point on circle with angle : A3 = 324
Solutions : Use calculator
  • r1 = cos(A1) + i*sin(A1)
  • r2 = cos(A2) + i*sin(A2)
  • r3 = cos(A3) + i*sin(A3)
  • r4 = cos(A4) + i*sin(A4)
  • r5 = cos(A5) + i*sin(A5)
Solutions : By constuctions
  • For angle A1 : r1 = x1 + i*y1. Measure x1 and y1
  • For angle A2 : r2 = x2 + i*y2. Measure x2 and y2
  • Similarly find other five solutions
  • Use the conjugate complex to reduce the calculation

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Q02. Solve x^5 - 1 = 0

De Moivre's Theory : Draw a unit circle
  • 1. Draw 1st point on circle with angle : A1 = 000
  • 2. Draw 2nd point on circle with angle : A2 = 072
  • 3. Draw 3nd point on circle with angle : A3 = 144
  • 4. Draw 4nd point on circle with angle : A3 = 216
  • 5. Draw 5nd point on circle with angle : A3 = 288
Solutions : Use calculator
  • r1 = cos(A1) + i*sin(A1)
  • r2 = cos(A2) + i*sin(A2)
  • r3 = cos(A3) + i*sin(A3)
  • r4 = cos(A4) + i*sin(A4)
  • r5 = cos(A5) + i*sin(A5)
Solutions : By constuctions
  • For angle A1 : r1 = x1 + i*y1. Measure x1 and y1
  • For angle A2 : r2 = x2 + i*y2. Measure x2 and y2
  • Similarly find other five solutions
  • Use the conjugate complex to reduce the calculation

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Q03. Solve x^5 + i = 0

De Moivre's Theory : Draw a unit circle
  • 1. Draw 1st point on circle with angle : A1 = 054
  • 2. Draw 2nd point on circle with angle : A2 = 126
  • 3. Draw 3nd point on circle with angle : A3 = 198
  • 4. Draw 4nd point on circle with angle : A3 = 270
  • 5. Draw 5nd point on circle with angle : A3 = 342
Solutions : Use calculator
  • r1 = cos(A1) + i*sin(A1)
  • r2 = cos(A2) + i*sin(A2)
  • r3 = cos(A3) + i*sin(A3)
  • r4 = cos(A4) + i*sin(A4)
  • r5 = cos(A5) + i*sin(A5)
Solutions : By constuctions
  • For angle A1 : r1 = x1 + i*y1. Measure x1 and y1
  • For angle A2 : r2 = x2 + i*y2. Measure x2 and y2
  • Similarly find other five solutions

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Q04. x^5 - i = 0

De Moivre's Theory : Draw a unit circle
  • 1. Draw 1st point on circle with angle : A1 = 018
  • 2. Draw 2nd point on circle with angle : A2 = 090
  • 3. Draw 3nd point on circle with angle : A3 = 162
  • 4. Draw 4nd point on circle with angle : A3 = 234
  • 5. Draw 5nd point on circle with angle : A3 = 306
Solutions : Use calculator
  • r1 = cos(A1) + i*sin(A1)
  • r2 = cos(A2) + i*sin(A2)
  • r3 = cos(A3) + i*sin(A3)
  • r4 = cos(A4) + i*sin(A4)
  • r5 = cos(A5) + i*sin(A5)
Solutions : By constuctions
  • For angle A1 : r1 = x1 + i*y1. Measure x1 and y1
  • For angle A2 : r2 = x2 + i*y2. Measure x2 and y2
  • Similarly find other five solutions

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Q05. Show that 0.30901 + 0.95106*i is a root of x^5 - 1 = 0

Proof
  • x^5 - 1 = (0.30901 + 0.95106*i)^5 - 1
  • = (0.30901)^5
  • + 05*((0.30901)^4)*((0.95106)^1)*i
  • + 10*((0.30901)^3)*((0.95106)^2)*(i^2)
  • + 10*((0.30901)^2)*((0.95106)^3)*(i^3)
  • + 05*((0.30901)^1)*((0.95106)^4)*(i^4)
  • + 01**((0.95106)^5)*(i^5)
  • - 1
  • = 0.002817 + 5*0.0091178*0.95106*i + 10*0.0295064*0.904515*(-1)
  • + 10*0.09548718*0.860248*(-i) + 5*0.30901*0.8181476*(+1) + 0.778107*(i) - 1
  • = 0.02817 + 0.0433578*i - 0.2668898 - 0.821426556*i + 1.2640789 + 0.778107*i - 1
  • = 0.0000 + 0.0000*i

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Q06.

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Q07.


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Q08.


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Q09. Answer

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Q10. Answer

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