What is the first part of the second step to prove that Sn=>3+8+15+...+ n(n-3)=n(n+1)(2n+7)/6​

can someone answer this question plz

step-by-step explanation:

trapezoid

step-by-step explanation:

first i plotted all my points on a grid graph

i made sure all of them were in the correct quadrant

then i saw it was a trapezoid or a quadrilateral

the image is given below

since the options are not given so we draw it from the equation

the given equation is

y = (x-1) (x+4)

y = y² + 3x - 4

the above equation is a quadratic equation which will have two roots. if we draw the graph for it, it will look like this