Question

what must be the unit of an angle if the sum of the measures of a degree and a grade is 1?

Answer 1

x+tan(x) = 1, perhaps?

Answer 2

1 degree = 9/10 grades.

If angle is x degrees. This means that angle is also 9x/10 grades

Sum of measure of angle in degree and grade=1
This means

x+9x/10 =1

Find x from here. It will be the measure of angle in degrees.

Answer 3

is that a british thing?

Answer 4

grade is a unit of angle. A right angle is equal to 100 grades.
I do not know if it is a english system.

Answer 5

yeah ... a grad is a "metric" unit back from when the english wanted to divvy up the right angle into 100 parts instead of 90