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Let \(k_1\ \text{and} \ k_2\) be two randomly selected natural numbers.

The probability that \((i)^{k_1}+(i)^{k_2}\) is non-zero is (where \(i=\sqrt{-1} )\)

(1) \(\frac{1}{2}\)

(2) \(\frac{3}{4}\)

(3) \(\frac{1}{4}\)

(4) \(\frac{1}{6}\)

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1 Answer

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by (50.3k points)
edited by

Correct option is (2) \(\frac{3}{4}\)  

\((i)^{k_1}+(i)^{k_2}\) is non zero

\(\Rightarrow k_1: 4 \lambda_1+r_1, \quad r_1 \in\{0,1,2,3\} \)   

\( K_2: 4 \lambda_2+r_2, \quad r_2 \in\{0,1,2,3\}\)      

The pairs to get zero will be 

\( (1,-1),(i,-i) \)

\(\Rightarrow \text { (i) }(1,-1) \text { pair } \)

\(\Rightarrow\left(r_1, r_2\right) \in\{(2,0),(0,2)\}\)  

(ii) (i, -i) pair  

\(\Rightarrow\left(r_1, r_2\right) \in\{(1,3),(3,1)\} \) 

\(\Rightarrow \text { probablity }\left(i^{k_1}+i^{k_2} \neq 0\right) \) 

\(= 1-\text { probablity }\left(i^{k_1}+i^{k_2} \neq 0\right) \)

\(= 1-\frac{4}{16}=\frac{12}{16}=\frac{3}{4}\)

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