Use the figure to the right to find the value of PT. T is the midpoint of PQ. PT=3x+6 and TQ=6x-9

Pranza plotted point a in the coordinate plane below.

Lin is writing an equation to model the proportional relationship between y, the total cost in dollars of downloading videos from a website, and x, the number of videos downloaded. she knows that the total cost to download 3 videos was $12. her work to find the equation is shown below. joylin’s work step 1 k= 3/12= 0.25 step 2 y= 0.25x where did joylin make her first error?

How do i simply this expression (quadratic formula basis) on a ti-84 or normal calculator?