Let f(x) = 2x + 50
The angle to this equation would be the coefficient "a''
Look:
f(x) = ax + b
Then,
To this question, a = 2
Always, a = Tg(angle)
That would be the slope of the line.
Tg(angle) = a
Tg(angle) = 2
Apply arctg on both the sides
ArcTg(Tg(angle) ) = Arctg(2)
Arctg(tg ) , They cancel
Angle = Arctg(2)
Calculate the Arctg(2) on the calculator
Angle = 63,43°