take derivatives which is the sum of derivatives which is simpler than this thing where if we have many complicated terms multiplied together they'd all like stay together in complicated ways and be a lot more hairy to work with and we can do this thing derivative respect to theta equal to 0 is what we want let's look at the derivative so N 1 times 1 over theta plus and 0 times 1 over 1 minus theta and then a negative 1 here that equal to 0 they were multiplying by theta and 1 minus theta so we have N 1 1 minus theta plus well -