13, 70, 71, 76, ?, 81, 86, 70, 91
70
71
80
96
None of these
In this series, 5 is added to the previous number; the number 70 is inserted as every third number.
Q60) Look at this series: 70, 71, 76, __, 81, 86, 70, 91, ... What number should fill the blank?
Show that the lines with direction cosines 1213, −313, −413; 413, 1213, 313; 313, −413, 1213 are mutually perpendicular.