matlab - Using a value from a matrix as a multiplier in an equation? -

started using matlab couple of weeks ago, don't know proper syntax / terminology.

i'm trying use value in 3x1 matrix multiplier in equation later.

this draw circle radius , centre point defined values input user.

i have pop-up window, values input user , stored in 3x1 cell (labelled answer).

how use second value of matrix, answer(2), in following equation:

x = 'answer(2)' * cos(theta) + xcentre;

this error message appears:

error using  .*  matrix dimensions must agree.  error in disks (line 40) x = 'answer(2)'.* cos(theta) + xcentre; 

in matlab, apostrophes ('') define string. if name of matrix answer, can refer second value command answer(2) mentioned @schorsch. more infos on vectors , matrices, can check this site.