Found the answer.
Wasted so much time typing =.=""
In my second equation
should beCode:3a-T=3gsin60Code:3a+T=3gsin60
What I did isA particle P of mass 8 kg rests on a smooth plane inclined at 30 degrees to the horizontal. It is connected by a light inextensible string passing over a smooth light pulley at the top of the plane, to a particle of mass 3kg which is on a smooth plane inclined at 60 degrees to the horizontal.
Find the acceleration of the system and the tension in the string.
Code:T-8a=8gsin30Code:3a-T=3gsin60
Used the calculator for simultaneous equation, which is not the answer in the back of the book. It should be 1.249m/s^2 and 29.21N. But i've got -64.25 and -12.9
many thanks for your help!