If sec 4A = cosec (A − 20°),

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Question:

If sec 4A = cosec (A − 20°), where 4A is an acute angle, find the value of A.

Solution:

Given that:

$\sec 4 A=\operatorname{cosec}\left(A-20^{\circ}\right)$, then we have to find the value of $A$

Since it is given that the angle 4A is acute angle, therefore we can apply the identity 

Therefore the given equation can be written as

$\operatorname{cosec}\left(90^{\circ}-4 A\right)=\operatorname{cosec}\left(A-20^{\circ}\right)$

$\Rightarrow \quad 90^{\circ}-4 A=A-20^{\circ}$

$\Rightarrow \quad 5 A=110^{\circ}$

$\Rightarrow \quad A=22^{\circ}$

Hence the value of A is 22°

 

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