Question

4. The three angles of the quadrilateral are 90°, 105°, 85°. Find the measure of the fourth angle of a quadrilateral.

Answer 1

Let the fourth be x

Now By angle sum property we have
$90 + 105 + 85 + x = 360 \\ 280 + x = 360 \\ x = 360 - 280 \\ x = 80$

Answer 2

let the fourth angle be x
90°+105°+85°+x =360°
280°+x=360°
x= 360°-280°
x=80°
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