Knowing that the angles of all triangle add up to 190 degrees, we can assume that 40 + 65 + x + 83 = 180 as well
x + 40 + 65 + 83 = 180
Now combine all like terms ( 40 + 65 + 83 )
x + 188 = 180
Now to get the value of x we need to isolate it in one side of the equation, we can do that by subtracting 188 from both sides of the equation:
x + 188 - 188 = 180 - 188
x = - 8
As we subtracted 188 from BOTH sides of the equation, the equation still is true
Answer: x = -8
I hope you understand it ;)
