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Consider the equation:

z^(4)=81
One solution is 
z=3, another is -3 , and there are 2 more distinct complex solutions.
What are those solutions?
Choose 
2 answers:
A 
z=3i
B 
z=27 i
c. 
z=-3i
D 
z=-27 i

Consider the equation:\newlinez4=81 z^{4}=81 \newlineOne solution is z=3 z=3 , another is 3-3 , and there are 22 more distinct complex solutions.\newlineWhat are those solutions?\newlineChoose 22 answers:\newlineA) z=3i z=3 i \newlineB) z=27i z=27 i \newlineC) z=3i z=-3 i \newlineD) z=27i z=-27 i

Full solution

Q. Consider the equation:\newlinez4=81 z^{4}=81 \newlineOne solution is z=3 z=3 , another is 3-3 , and there are 22 more distinct complex solutions.\newlineWhat are those solutions?\newlineChoose 22 answers:\newlineA) z=3i z=3 i \newlineB) z=27i z=27 i \newlineC) z=3i z=-3 i \newlineD) z=27i z=-27 i
  1. Rewrite as Difference of Squares: Recognize that the equation z4=81z^{4}=81 can be rewritten as z481=0z^{4} - 81 = 0, which is a difference of squares.
  2. Factor using Formula: Factor the equation using the difference of squares formula, which states that a2b2=(a+b)(ab)a^2 - b^2 = (a + b)(a - b). In this case, we have z481=(z2+9)(z29)z^{4} - 81 = (z^2 + 9)(z^2 - 9).
  3. Further Factorization: Notice that z29z^2 - 9 is also a difference of squares, so we can factor it further to (z+3)(z3)(z + 3)(z - 3). Now we have (z2+9)(z+3)(z3)=0(z^2 + 9)(z + 3)(z - 3) = 0.
  4. Find Solutions for z2+9z^2 + 9: We already know that z=3z = 3 and z=3z = -3 are solutions from the factors (z3)(z - 3) and (z+3)(z + 3). Now we need to find the solutions for z2+9=0z^2 + 9 = 0.
  5. Solve for zz: Solve the equation z2+9=0z^2 + 9 = 0 for zz. Subtract 99 from both sides to get z2=9z^2 = -9.
  6. Complex Solutions: Take the square root of both sides to solve for zz. The square root of 9-9 is 3i3i and 3i-3i, so z=3iz = 3i and z=3iz = -3i are the complex solutions.
  7. Check Validity: Check the solutions by substituting them back into the original equation z4=81z^{4}=81. For z=3iz = 3i, (3i)4=81i4=81(1)2=81(3i)^{4} = 81i^{4} = 81(-1)^{2} = 81, which is true. For z=3iz = -3i, (3i)4=81i4=81(1)2=81(-3i)^{4} = 81i^{4} = 81(-1)^{2} = 81, which is also true.

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