The function is increasing when the first derivative is positive, and
it is decreasing .... negative
dy/dx = -12x^2 + 30x + 18
consider the graph of y = -12x^2 + 30x +18
it is a parabola opening down with x-intercepts at x = 3 and x = -1/2
So the function is
increasing for -1/2 < x < 3
decreasing for x<-1/2 or x > 3
confirmation:https://www.wolframalpha.com/input/?i=+y+%3D+%E2%88%924x%5E3%2B15x%5E2+%2B+18x+%2B+3+from+-2+to+6
Find the intervals of increase and decrease algebraically for:
Y = −4x³+15x²+ 18x + 3
2 answers
Thank you