Question

Sin A = Cos (A-20) where 4A is an acute angle find the value of A

Answer 1

Sin A = Cos (A-20)

we know...
sin A = cos(90-A)

=> Sin A = Cos (A-20)

=> sin A= cos(90-A)=cos(A-20)

=> cos(A-20)=cos(90-A)

=>A-20=90-A

=>2A=90+20

=>2A=110

=>A=110/2=55

thus... A=55

hope it helps you...
☺☺

Answer 2

Your question needs a correction,

'A is an acute angle ' is written wrong '4A is am acute angle '





$\textbf{solution : - }$


sinA = cos( A - 20 )

$cos( 90 - A ) = cos( A - 20 ) \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \bold{ | \: sin \theta \: = cos(90 - \theta)}$


90 - A = A - 20

=> 90 + 20 = A + A

=> 110 = 2A

$= > \frac{110}{2} = A$

=> 55 = A