Question

the three angles of a quadrilateral 60 degrees, 80 degrees and 120 degrees find the fourth angle

Answer 1

sum of angles of a quadrilateral=360°
let the unknown angle of quadrilateral be X
60 +80+120+X =360
260+X=360
X= 360-260
therefore X =100

Answer 2

Let < A = 60°, <B = 80°, <C = 120°, <D = to find
the sum of all angles of quadrilateral is 360°
<A + <B + <C + <D = 360°
60° + 80° + 120° + < D = 360°
260° + <D = 360°
<D = 360° - 260° = 100°
the fourth angle is 100°