solutions of coupled differential equations

Hi.

my equations are like this form

(1-x)y'+(1-y)z'=0
(i-1)x'+z*y'=0
x=1-cos(50*t)
m_cp=50(5*y'-4x')
m_p=(i-1)*(4.8*z')

i am having more than fifty equations like this where x',y',z' are function of t. i don't know how to solve these group of equations . i suspects that these groups are solved by ode15s by extracting mass matrix but i am unable to develop mass matrix,please help .

else if it will be solved by any other method please tell me as my numbers of equations are more if i will not take help of any built in solver it is very difficult to solve .

thanks in advance...............