Question
If $\tan\text{A}+\cot\text{A}=4,$ then write the value of $\tan^4\text{A}+\cot^4\text{A}.$

Answer

$(\tan\text{A}+\cot\text{A})^2=\tan^2\text{A}+\cot^2\text{A}+2\tan\text{A}\cot{A}$ $16=\tan^2\text{A}+\cot^2\text{A}+2$ $\tan^2\text{A}+\cot^2\text{A}=14$ $(\tan^2\text{A}+\cot\text{A})^4=\tan^4\text{A}+1\tan^3\text{A}\cot\text{A}6\tan^2\text{A}\cot^2\text{A}+4\tan\text{A}\cot^3\text{A}+\cot^4\text{A}$ $256=\tan^4\text{A}+4(\tan^2\text{A}+\cot^2\text{A})+\cot^4\text{A}+6$ $256=\tan^4\text{A}+4(14)+\cot^4\text{A}+6$ $\tan^4\text{A}+\cot^4\text{A}=194$

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