Use the information in the figure to find x

Explanation

Strategy We will write an equation involving x that mathematically models the situation.

WHY We can then solve the equation to find the unknown angles measures.

Solution

Since the sum of the measures of the two adjacent angles is 80^o, we have

• The word sum indicates addition
  • x + 35^o = 80^o
• To isolate x, undo the addition of 35^o by subtracting 35^o from both sides
  • x + 35^o - 35^o = 80^o - 35^o
• Do the subtractions: 35^o - 35^o = 0^o and 80^o - 35^o = 45^o

Thus, x is 45^o.  As a check, we see that 45^o + 35^o = 80^o