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Connecting
Math: Just for Fun #19 |
There is one function f:[-1,1]->R,
defined like this:
f(x)=x*x+m*x+n for x in [-1,0) and
f(x)=p*x*x+4*x+4 for x in [0,1]
and m,n,p in R. To be find the parameters m, n, p so as the function f
verify the conditions of theoreme's Rolle on the interval [-1,1].
For f to be in conditions of theorem's
Rolle she must be continue on [-1,1], derivate on (-1,1) and f(-1)=f(1)
f_s(0)=lim f(x)=lim(x*x+m*x+n)=n
x->0 x->0
x<0 x<0
f_d(0)=lim lim f(x)=lim(p*x*x+4*x+4)=4
x->0 x->0
x>0 x>0
f(0)=4
==>n=4==>
f(x)=x*x+m*x+4 for x in [-1,0)
f(x)=p*x*x+4*x+4 for x in [0,1]
f'_s(0)=lim f'(x)=lim(2*x+m)=m
x->0 x->0
x<0 x<0
f'_d(0)=lim lim f'(x)=lim(2*p*x+4)=4
x->0 x->0
x>0 x>0
==> m=4
==> f(x)=x*x+4*x+4 for x in [-1,0]
and f(x)=p*x*x+4*x+4 for x in [0,1]
But f(-1)=f(1)==>p=-7
So, n=4,m=4,p=-7
By Camelia Sima
Teacher: Ligia Garlea
"Alex. Papiu Ilarian" HS Dej, Cluj,
Romania
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