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Trigonometrical Equations
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If $tanA + cotA = 4$, then $tan^4A + cot^4A$ is equal to
A
$110$
B
$191$
C
$80$
D
$194$
Solution
$(\tan A+\cot A)^{2}=16$
$\Rightarrow \quad \tan ^{2} A+\cot ^{2} A+2=16$
$\Rightarrow \quad \tan ^{2} A+\cot ^{2} A=14$
$\Rightarrow \quad\left(\tan ^{2} A+\cot ^{2} A\right)^{2}=196$
$\Rightarrow \quad \tan ^{4} A+\cot ^{4} A+2=196$
$\Rightarrow \quad \tan ^{4} A+\cot ^{4} A=194$
Standard 11
Mathematics