According to Corresponding Angles Theorem, given one pair of parallel lines cut by another transversal one, the pair of corresponding angles have the same measure.
Therefore:
Geometrically proving:
Since the angle is 80º then we can state its Alternate Interior angle (in blue) values also 80º. In addition to this, the Vertex Angle Theorem confirms that.
Algebraically, just plug in 30º for x, then solve it to prove it:
The angle of 80 degrees is the same angle as the one with the equation. That equation has to equal 80 somehow. ------------------------------------------ 80 - 20 (from equation) = 60 60 ÷ 2 (also from equation) = 30 -------------------------------------------- x = 30 To make sure plug it in (2 x 30)+ 20 60 + 20 = 80 --------------- x should equal 30
What when multiplied is +3 but when added is 4? 3 and 1. You then get (x+3)(x+1) is the first part of the answer. If you want to find x, set x+3 to 0. x+3=0. Then subtract 3 from both sides to get x by itself. x= -3. Do the same with the x+1.