The marginal cost C of manufacturing x golf clubs may be expressed by the quadratic function C(x) = 3.5x² - 310x + 23,000

How many clubs should be manufactured to minimize the marginal cost?

δabc ≅ δdcb by sas because

db ≅ ac . . given (side)

bc ≅ bc . . reflexive property (side)

∠dbc ≅ ∠ acb . . alternate interior angles where transversal bc crosses parallel lines bd and ac (included angle)

but there’s no any figure there!