What is the maximum value of the expression -5r^2 + 40r - 12 for real r?
Use the quadratic formula to solve for r. Then sub both values of r into your equation and see which one gives a higher value.
This is a dome shaped parabola (due to the negative coefficient of the x^2 term)
the r value at the max point will be given by -b /2a where a =-5 b = 40 sooooooo r = ?
Once you FIND this r value, sub in to the equation to find the max value of the expression.... You CAN do it !