>>27
-5-13 = -18
(-2)^2 ÷(-6)^2 ×9 = 4÷36×9 = 1
(√6)×(√8) - (√50) ÷(√2) = (4√3) - 5
-(1/2) + (-2/3) = -(3/6) -(4/6) = -7/6