Answer:
[tex]\large \boxed{\sf \ \ \dfrac{8}{7} \ \ }[/tex]
Step-by-step explanation:
Hello, please consider the following.
The solutions are, for a positive discriminant:
[tex]\dfrac{-b\pm\sqrt{\Delta}}{2a} \ \text{ where } \Delta=b^2-4ac[/tex]
Here, we have a = -21, b = -11, c = 40, so it gives:
[tex]\Delta =b^2-4ac=11^2+4*21*40=121+3360=3481=59^2[/tex]
So, we have two solutions:
[tex]x_1=\dfrac{11-59}{-42}=\dfrac{48}{42}=\dfrac{6*8}{6*7}=\dfrac{8}{7} \\\\x_2=\dfrac{11+59}{-42}=\dfrac{70}{-42}=-\dfrac{14*5}{14*3}=-\dfrac{5}{3}[/tex]
We only want x > 0 so the solution is
[tex]\dfrac{8}{7}[/tex]
Hope this helps.
Do not hesitate if you need further explanation.
Thank you
