Answer :

Answer:

The correct answer is option

[tex]d.\ x=-i, i, 3 \sqrt{5}\ or\ -3 \sqrt{5}[/tex]

Step-by-step explanation:

The given equation has a degree 4 (Highest power of [tex]x[/tex]):

[tex]x^4-44x^2-45=0[/tex] is the given equation which can be written as:

[tex](x^2)^2-44x^2-45=0 ...... (1)[/tex]

Let [tex]t=x^{2}[/tex] and putting it in equation (1):

[tex]t^2-44t-45=0 \\[/tex]

Solving the above quadratic equation in variable [tex]t[/tex]:

[tex]\Rightarrow t^2-45t+t-45=0 \\\Rightarrow t(t-45)+1(t-45)=0\\\Rightarrow (t+1)(t-45)=0\\\Rightarrow t =-1\ or\ 45[/tex]

We know that [tex]t=x^{2}[/tex]

So, [tex]x^{2} =-1\ or\ x^{2}= 45[/tex]

1. Solving [tex]x^{2} =-1[/tex]

[tex]\Rightarrow x = +\sqrt{-1}\ or\ -\sqrt{-1}\\\Rightarrow x = i\ or\ -i[/tex]

2. Solving [tex]x^{2} =45[/tex]

[tex]\Rightarrow x = +\sqrt{45}\ or\ -\sqrt{45}\\\Rightarrow x = 3\sqrt{5}\ or\ -3\sqrt{5}[/tex]

Hence, correct answer is:

[tex]x=-i, i, 3 \sqrt{5}\ or\ -3 \sqrt{5}[/tex]

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Rewritten by : Barada