What substitution should be used to rewrite 4x^4-21x^2+20 =0 as a quadratic equation

How many sides does a regular polygon have if each exterior angle measure is 45 degrees explain your answer, i really don't understand this.

The numbers on a football field indicate 10 yard increments. you walk around the perimeter of a football field between the pylons. you walk a distance of 30623 yards. find the area and perimeter of the indicated regions. write your answers as mixed numbers, if necessary. a. one end zone: perimeter: yd area: yd2 b. the playing field (not including end zones): perimeter: yd area: yd2 c. the playing field (including end zones): perimeter: yd area: yd2

Which equation represents a line that passes through the point (9, -4) and has a slope of 3/5?