Question 724517
To determine the appropriate landing speed of an airplane, the formula D=.1x−3x+22 is used, where x is the initial landing speed in feet per second and D is the distance needed in feet.
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I think this should be D = .1x^2 - 3x + 22
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If the landing speed is too fast, the pilot may run out of runway; if the speed is too slow, the
plane may stall. What is the appropriate landing speed if the runway is 800 feet long?
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.1x^2 - 3x + 22 = 800
.1x^2 - 3x + 22 - 800 = 0
.1x^2 - 3x - 778 = 0
solve this using the quadratic formula
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
this equation:
{{{x = (-(-3) +- sqrt(-3^2-4*.1*-778 ))/(2*.1) }}}
You can do the math, I got x = 104.47 mph