Solve Matrix without Calculator: Find Values of X

[jjuugg]

hello~ I forgot how to do matrix without a calculator.

I think it was like crossing across and down and then add all of them?

i think... but i wasn't sure.

so could anybody explain how to do matrix with hands?

also, is this problem solvable without a calculator?

find all values of x that make l 2 -1 4 l
l 3 0 5 l = l x 4 l
l 4 1 6 l l 5 x l

and the answer is + or- 4.47

thank you for reading my questions!~><

 

[Defennder]

I don't understand your notation at all. Are you supposed to find the determinant of the matrix or solve a system of linear equations?