Answer:
a = 14
Step-by-step explanation:
The consecutive angles in a parallelogram are supplementary, sum to 180°
a² - 10a + 7a + 26 = 180
a² - 3a + 26 = 180 ( subtract 180 from both sides )
a² - 3a - 154 = 0 ← in standard form
(a - 14)(a + 11) = 0 ← in factored form
Equate each factor to zero and solve for a
a - 14 = 0 ⇒ a = 14
a + 11 = 0 ⇒ a = - 11
Since a > 0 , then a = 14
