Question

If sec4A = cosec(A-10) and 4A is acute then ∠A = ? (a) 20 (b) 30 (c) 30 (d) 50

Answer 1

sec4A =cosec(A-10)
sec4A=sec(90-(A-10)
sec4A=sec(90-A+10)
sec = sec
so sec is divide by sec
so sec =0
therefore
4A=90-A+10
4A=100-A
4A+A=100
5A=100
A=
$\frac{100}{5} = 20$