Answer:
∠DBC = 155°
Explanation:
Assuming that ABC is a straight line.
Angles on a straight line sum to 180°.
⇒ (2x² + 3x - 2) + ∠DBC = 180°
⇒ ∠DBC = 180° - (2x² + 3x - 2)
The sum of the interior angles of a triangle is 180°:
⇒ (x² + 1) + (4x + 3) + ∠DBC = 180°
⇒ ∠DBC = 180° - (x² + 1) - (4x + 3)
Therefore, we can equate the equations and solve for x:
⇒ ∠DBC = ∠DBC
⇒ 180 - (2x² + 3x - 2) = 180 - (x² + 1) - (4x + 3)
⇒ 180 - 180 = (2x² + 3x - 2) - (x² + 1) - (4x + 3)
⇒ (2x² + 3x - 2) - (x² + 1) - (4x + 3) = 0
⇒ 2x² + 3x - 2 - x² - 1 - 4x - 3 = 0
⇒ x² - x - 6 = 0
⇒ x² + 2x - 3x - 6 = 0
⇒ x(x + 2) - 3(x + 2) = 0
⇒ (x + 2)(x - 3) = 0
Therefore, x = -2, x = 3
As angles are positive, x = 3 only
Substituting found value of x into the angle expressions:
⇒ ∠BDC = x² + 1 = (3)² + 1 = 10°
⇒ ∠DCB = 4x + 3 = 4(3) + 3 = 15°
The sum of the interior angles of a triangle is 180°:
⇒ ∠DBC + ∠BDC + ∠DCB = 180°
⇒ ∠DBC = 180° - ∠BDC - ∠DCB
⇒ ∠DBC = 180° - 10° - 15°
⇒ ∠DBC = 155°