Sunday, August 12, 2012

Given f(x)=-3x^2-7x+19 and g(x)=2x^2-4x-5 find the following:a. (f-g)(-2) b. (fg)(-2) c. (g°f)(-2) d. g-1(-2) e. f(g(f(2)))Supposedly there are...

a) (f-g)(x) =
(-3x^2-2x^2)+(-7x+4x)+(19+5)


(f-g)(x) =
-5x^2-3x+24



b) For calculating (fg)(-2), we'll
calculate first the product (fg)(x).


(fg)(x)= (-3x^2-7x+19
)*(2x^2-4x-5)


We'll multiply each term from the first
bracket with each term from the second one and the resul will
be:


(fg)(x)=
-6x^4+12x^3+15x^2-14x^3+28x^2+35x+38x^2-76x-95


We'll group
the terms which have the same unknown raised to the same
degree;


(fg)(x)=
-6x^4+x^3(12-14)+x^2*(15+28+38)+x*(35-76)-95


(fg)(x)= -6x^4
- 2x^3 + 52x^2 -41x -95


Now, we'll calculate fg(-2), by
substituting x with the value (-2):


(fg)(-2)= -6(-2)^4 -
2(-2)^3 + 52(-2)^2 -41(-2) -95


(fg)(-2)=
-96+16+186-95


(fg)(-2)=
-11



c) To calculate (g°f)(-2),
first we have to calculate (g°f)(x).


(g°f)(x) = g(f(x)) =
2*[f(x)]^2-4*f(x)-5


g(f(x))=2(9x^4+49+x^2+361-42x^3-57x^2-133x)+12x^2+28x-81


g(f(2))=
2(144+196+361-336-228-266)+48+56-81


g(f(2))=
-235



d) (g-1)(x) =
2x^2-4x-5-1


(g-1)(x) =
2x^2-4x-6


We'll calculate (g-1)(x) as we have calculated
f-g, but this time having a constant function =1, instead a mono variable
function.


(g-1)(-2) =
2(-2)^2-4(-2)-6


(g-1)(-2) =
8+8-6


(g-1)(-2) =
16-6


(g-1)(-2) =
10



e. For calculating f(g(f(2))),
we'll use the result from the point c), where we've calculated already g(f(2))=
-235.


So, we'll have to calculate
f(-235).


f(-235) = -3(-235)^2 - 7(-235) +
19


f(-235) = -165675 + 1645 +
19


f(-235) =
-164011

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