For each of the equations given below, use the discriminant to decide how many real roots the equation has. \[ \begin{array}{l} 2 x^{2}-9 x+1=0[\text { Select }] \\ 3 x^{2}-2 x+7=0[\text { Select }] \\ 6 x^{2}-x-10=0[\text { S Select }] \\ 4 x^{2}+12 x+9=0[\text { Select }] \\ x^{2}+3 x+5=0[\text { Select }] \end{array} \]

Solve the equation. Check your solutions. (Enter your answers as a comma-separated list. \[ 6 x^{4}-54 x^{2}=0 \] \( x=\square \)

Solve the equation. Check your solutions. \[ 9 x-3 \sqrt{x}-2=0 \]

\( y = \sqrt { 1 - \sin x } + \operatorname { lan } ^ { 4 } ( x ^ { 2 } + 1 ) \)

8.3 จงหาฟังก์ชันเมื่อกำหนดค่าความยืดหยุ่นมาให้เป็น \( E=-\frac{0.2 P^{2}}{Q} \) และเมื่อราคาเป็น 15 บาทต่อหน่วย อุปสงค์เป็น 100 หน่วย

A sprinter runs around a 400 m running track twice (distance \( =800 \mathrm{~m} \) ). They start in lane 1 and finish in lane 1 (start and finish in the same position). They complete the run in 2 min 20 sec . Calculate their average velocity (not speed!) and include the unit \( (\mathrm{m} / \mathrm{s}) \) ?