hello everyone,i have solved over 800 problems of varying difficulty here but still i am not progressing that much. Can someone please suggest me proper guidelines or point out the mistakes which i am doing by looking in my profile.!!!! i need help from this community,plz.

116312856 problem:840D I am using square root decomposition here.Can anyone help to resolve the issue.

can anyone please help me out as i am always stuck in this part.