Powers of the imaginary unit (article) | Khan Academy (2024)

Learn how to simplify any power of the imaginary unit i. For example, simplify i²⁷ as -i.

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  • satyanash

    8 years agoPosted 8 years ago. Direct link to satyanash's post “How is `i^3 = -i` ?My un...”

    How is i^3 = -i ?
    My understanding leads me to:

    i^3 = i * i * i
    i^3 = sqrt( -1 ) * sqrt( -1 ) * sqrt( -1 ) ; i = sqrt( -1 )
    i^3 = sqrt( -1 * -1 * -1 )
    i^3 = sqrt( -1 )
    i^3 = i

    (53 votes)

    • andrewp18

      8 years agoPosted 8 years ago. Direct link to andrewp18's post “On step 3 you did:√𝑎 • ...”

      Powers of the imaginary unit (article) | Khan Academy (4)

      Powers of the imaginary unit (article) | Khan Academy (5)

      Powers of the imaginary unit (article) | Khan Academy (6)

      On step 3 you did:
      √𝑎 • √𝑏 = √(𝑎𝑏)
      But that is only true if:
      𝑎, 𝑏 > 0
      Which is not the case here. Comment if you want to see a proof of that.

      (160 votes)

  • Jonathan Huang

    7 years agoPosted 7 years ago. Direct link to Jonathan Huang's post “Where do you use this in ...”

    Where do you use this in the real world?

    (15 votes)

    • 🎓 Arnaud Jasperse

      7 years agoPosted 7 years ago. Direct link to 🎓 Arnaud Jasperse's post “Physics uses it. Electric...”

      Powers of the imaginary unit (article) | Khan Academy (10)

      Powers of the imaginary unit (article) | Khan Academy (11)

      Physics uses it. Electrical Engineering often have to use the imaginary unit in their calculations, but it is also used in Robotics. There, to rotate an object through 3 dimensions they even result in using Quaternions (which build on the imaginary unit i).

      (32 votes)

  • dollyrauh

    8 years agoPosted 8 years ago. Direct link to dollyrauh's post “Hi, could someone maybe h...”

    Hi, could someone maybe help me with what I did wrong in the last challenge problem? I followed along with their explanation well enough, but I'm scratching my head as to exactly where I messed up the problem. My answer was i, while the correct was -i. Also, by way of explanation, in steps three, four, and five, I am assuming that 1 can be rewritten as 1=sqrt(1) because 1*1= 1, therefore the square root of 1 equals 1.

    i^-1=

    1/i^1 (because properties of negative exponents)
    1/i (because i^1=i)
    1/sqrt(-1) (because i=sqrt(-1))
    sqrt(1)/sqrt(-1) (because the 1 in the numerator can be rewritten as sqrt(1) without changing its value)
    sqrt(1/-1) (to simplify inside the square root)
    sqrt(-1) (because 1/-1 is -1)
    sqrt(-1)=i (because i=sqrt(-1))
    =i

    It's driving me crazy that I can't figure out what I did wrong!! Please help.

    Thanks so much!!

    (14 votes)

    • Dominik.Ehlert

      8 years agoPosted 8 years ago. Direct link to Dominik.Ehlert's post “It seems to me your probl...”

      Powers of the imaginary unit (article) | Khan Academy (15)

      Powers of the imaginary unit (article) | Khan Academy (16)

      It seems to me your problem is the definition i = sqrt(-1). Better use i^2 = -1. You can see, that your last step would get you sqrt(-1) = +/- i, so the right solution is at least within, but the problem is better solved another way:
      i ^ (-1) = 1/i = 1/i * i/i <-- Expand with i
      = i/(i^2) <-- Multiply
      = i/(-1) <-- Definition
      = -i <-- Simplify
      Therefore i^(-1) = -i

      (33 votes)

  • joey mizrahi

    8 years agoPosted 8 years ago. Direct link to joey mizrahi's post “how is i^-1 = -idoesnt i...”

    how is i^-1 = -i
    doesnt it equal 1/i

    (7 votes)

    • Jacky Xie

      8 years agoPosted 8 years ago. Direct link to Jacky Xie's post “Yes, i^-1 = 1/i.Notice t...”

      Powers of the imaginary unit (article) | Khan Academy (20)

      Yes, i^-1 = 1/i.
      Notice that you can multiply 1/i by i/i, which gives you i/-1, or -i, which is much easier to comprehend than 1/i.

      (20 votes)

  • Rob

    8 years agoPosted 8 years ago. Direct link to Rob's post “will i^0=1?”

    will i^0=1?

    (9 votes)

    • Abhishek Kumar

      5 years agoPosted 5 years ago. Direct link to Abhishek Kumar's post “Hey, the explanation to y...”

      Hey, the explanation to your query is "any number other than 0 taken to the power 0 is defined to be 1".
      So i=√-1, "i" here is a real number. So i^0=1.
      It is explained in great detail at this website-->
      (though it requires some math, though eventually, you get the idea)
      http://mathworld.wolfram.com/Power.html
      However, "zero to the power of zero" (or 0^0) is undefined.

      (6 votes)

  • Peu255

    a year agoPosted a year ago. Direct link to Peu255's post “where are the powers of t...”

    where are the powers of the imaginary unit? I've seen no powers. Does it throw fireballs?

    (13 votes)

  • O Madhu 💞

    a year agoPosted a year ago. Direct link to O Madhu 💞's post “I understand how to solve...”

    I understand how to solve for i using simple negative exponents, but I don't know how you would solve for more larger negative exponents.

    (1 vote)

    • Tanner P

      a year agoPosted a year ago. Direct link to Tanner P's post “I’ll walk you through an ...”

      Powers of the imaginary unit (article) | Khan Academy (29)

      I’ll walk you through an example.

      Say you want to evaluate i^-207

      1. Divide by four and find the remainder
      207/4 = 51 R 3

      Since the remainder is 3, i^-207 = i^-3

      To see why this works: Using exponent properties, you can rewrite the problem as
      (i^4)^-51 * i^-3
      =1^-51 * i^-3
      =1 * i^-3
      =i^-3

      2. Now, this is something you know how to solve
      i^-3
      =1/i^3
      =1/-i
      =1/-i * i/i
      =i/-i^2
      =i/-(-1)
      =i/1
      =i.

      i^-207 = i

      (19 votes)

  • umairansari16

    7 years agoPosted 7 years ago. Direct link to umairansari16's post “what Will be i to the pow...”

    what Will be i to the power i 899999

    (4 votes)

    • kubleeka

      7 years agoPosted 7 years ago. Direct link to kubleeka's post “i^899999(i^900000)/i1/i...”

      Powers of the imaginary unit (article) | Khan Academy (33)

      i^899999
      (i^900000)/i
      1/i
      i/(i^2)
      i/(-1)
      -i

      (12 votes)

  • owengeorge

    a year agoPosted a year ago. Direct link to owengeorge's post “Is there any reason to us...”

    Is there any reason to use multiple of 4 over multiple of 1,2 etc or is just arbitrary?

    (4 votes)

    • Kim Seidel

      a year agoPosted a year ago. Direct link to Kim Seidel's post “It must be 4. It is not a...”

      Powers of the imaginary unit (article) | Khan Academy (37)

      It must be 4. It is not arbitrary. The powers of i rotate thru 4 values, not something else.
      i^1 = i
      i^2 = -1
      i^3 = -i
      i^4 = 1
      Then this pattern repeats
      i^5 = i
      i^6 = -1
      i^7 = -i
      i^8 = 1
      etc.

      Hope this helps.

      (11 votes)

  • tue99452

    7 years agoPosted 7 years ago. Direct link to tue99452's post “what is the answer of i ^...”

    what is the answer of i ^ i ?

    (6 votes)

    • Ron Joniak

      7 years agoPosted 7 years ago. Direct link to Ron Joniak's post “Well, due to a property t...”

      Well, due to a property that you might learn later, i = e^(i*pi/2). So, i^i = e^(i*pi/2*i). We know i*i = -1, so i^i = e^(-pi/2).

      i^i is always a real number, but there are some problems with this definition based on the property.

      (4 votes)

Powers of the imaginary unit (article) | Khan Academy (2024)

FAQs

What are imaginary powers? ›

Powers of Imaginary and Complex Numbers

These are the powers of the imaginary unit. i0=1i1=ii2=−1i3=−ii4=1 Notice that the even powers result in real numbers and odd powers give us imaginary numbers. There is a repeating pattern of 1,i,−1,−i when taking powers of i, starting with i0.

How to calculate i in math? ›

They are also defined as the square root of negative numbers. An imaginary number is the product of a non-zero real number and the imaginary unit "i" (which is also known as "iota"), where i = √(-1) (or) i2 = -1.

How does the power of i work? ›

Imaginary Number: The imaginary number i is defined by i 2 = − 1 . Any power of i is equal to either i, -1, -i, or 1.

What are the rules for the powers of i? ›

The powers of i is always equal to either one of these 4 numbers: 1, i , -1,-i. Here we will see why. i0 = 1, this is because for any non-zero number, any number with exponent 0 is equal to 1.

What is imaginary power called? ›

This “phantom power” is called reactive power, and it is measured in a unit called Volt-Amps-Reactive (VAR), rather than watts. The mathematical symbol for reactive power is (unfortunately) the capital letter Q.

What are the three types of powers? ›

Three types of powers the national government has:
  • Expressed Powers.
  • Implied Powers.
  • Inherent Powers.

What is the i rule? ›

"I before E, except after C" is a mnemonic rule of thumb for English spelling. If one is unsure whether a word is spelled with the digraph ⟨ei⟩ or ⟨ie⟩, the rhyme suggests that the correct order is ⟨ie⟩ unless the preceding letter is ⟨c⟩, in which case it may be ⟨ei⟩.

How does power work in physics? ›

Power is the rate at which work is done. In this case, rate means per unit of time. Power is calculated by dividing the work done by the time it took to do the work.

What are the imaginary rules? ›

An imaginary number is the product of a real number and the imaginary unit i, which is defined by its property i2 = −1. The square of an imaginary number bi is −b2. For example, 5i is an imaginary number, and its square is −25. The number zero is considered to be both real and imaginary.

What is the correct law for powers of powers? ›

The 'power of a power law of exponents' is used to simplify expressions of the form (am)n. This rule says, "When we have a single base with two exponents, just multiply the exponents." The two exponents are available one over the other. These can be conveniently multiplied to make a single exponent.

What is the 40th law of power? ›

40. Despise the Free Lunch. Don't accept things that people give to you for free. People will think they have power over you if you do.

How to raise to an imaginary power? ›

What if we want to raise other numbers to the power i? We can use the following relationship: ax=(elna)x=exlna. Using base 2 and exponent i, we get 2i=eiln2=cosln2+isinln2≈0.7692+0.6390i. (This is actually the principal value of 2 to the i power, there are other values which are possible.)

What is the imaginary part of power? ›

The imaginary current\power is the out of phase current circulating relative to the voltage. This is typically an issue when AC motors are used, which is quite frequent. Most AC motors are inductive.

What are the most uncommon powers? ›

Rare power
  • Omnipotence.
  • Superior Mystic Human Physiology.
  • Neverness Manipulation.
  • Temporal Erasure.

What is an imaginary creature with magical powers? ›

A fairy is an imaginary creature with magical powers. Fairies are often represented as small people with wings.

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