Question

3) Consider the sequence -11 ; 2sin3x ; 15; ...

3.1.1) Determine the values of x in the interval [0 ; 90] for whichthe sequence will be arithmetic. ​

Answer 1

First term=a=-11
U1=a=-11
U3=a+2d=15
-11+2d=15
2d=26
d=13
2sin3x - (-11)=d
2sin3x=2
sin3x=1
sin(3x)=sin(90)
3x=90
x=30 degrees