An arithmetic sequence starts at 200 and has common difference -50. Written in slope-intercept form, what is its explicit formula?

1. In slope-intercept form the slope is the common difference, so the coefficient of n is -50. 2. The vertical intercept is found by subtracting the common difference from the first term. 3. That gives 200 - (-50) = 200 + 50 = 250. 4. So the formula is a_n = -50n + 250. 5. Checking n = 1 gives -50 + 250 = 200, which is the first term, so the formula is right. 6. Using 200 as the intercept would put the first term at 150, which is the trap in that option. 7. Adding rather than subtracting the common difference gives 150, and flipping the sign of the slope reverses the whole sequence. _Source: OpenStax Algebra and Trigonometry (CC BY 4.0), Ch 13 "Sequences, Probability and Counting Theory", section 13.2 Arithmetic Sequences_