Given that x 2 − 5 x + 4 is a factor of the expression 2 x 4 + h x 3 + k x 2 + 3 4 x − 2 4 . What is the factorized form of the expression?
Hint: Find the values of h and k first.
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Great solution, sir.
If we look at the option, then the coefficient of x 4 − ( 2 ) could be get in option 4 only.As in other option we would get 3 , 6 , 3 as a coefficient of x 4
That's what I did.. The options were very poorly framed.
A solution that doesn't require you to find the values of h and k :
Since x 2 − 5 x + 4 is a factor of the expression, we can say that
( x 2 − 5 x + 4 ) ( a x 2 + b x + c ) = 2 x 4 + h x 3 + k x 2 + 3 4 x − 2 4
for some constants a , b and c . Expand the left hand side:
a x 4 + ( b − 5 a ) x 3 + ( 4 a − 5 b + c ) x 2 + ( 4 b − 5 c ) x + 4 c = 2 x 4 + h x 3 + k x 2 + 3 4 x − 2 4
Compare the terms of the expressions:
a x 4 = 2 x 4 ⟹ a = 2 4 c = − 2 4 ⟹ c = − 6 ( 4 b − 5 ( − 6 ) ) x = 3 4 x 4 b + 3 0 = 3 4 4 b = 4 ⟹ b = 1
Therefore,
2 x 4 + h x 3 + k x 2 + 3 4 x − 2 4 = ( x 2 − 5 x + 4 ) ( 2 x 2 + x − 6 ) = ( x − 1 ) ( x − 4 ) ( 2 x − 3 ) ( x + 2 )
Let f ( x ) = 2 x 4 + h x 3 + k x 2 + 3 4 x − 2 4 .
We know,
x 2 − 5 x + 4 = ( x − 1 ) ( x − 4 )
Since x 2 − 5 x + 4 is a factor of f ( x ) , it follows that ( x − 1 ) and ( x − 4 ) are factors of f ( x ) .
Thus,
f ( 1 ) = 0 a n d f ( 4 ) = 0 .
f ( 1 ) = 2 ( 1 ) 4 + h ( 1 ) 3 + k ( 1 ) 2 + 3 4 ( 1 ) − 2 4 = 0 ⟶ ( 1 ) f ( 4 ) = 2 ( 4 ) 4 + h ( 4 ) 3 + k ( 4 ) 2 + 3 4 ( 4 ) − 2 4 = 0 ⟶ ( 2 )
From ( 1 ) : h + k = 1 2 = 0 ⟶ ( 3 )
From ( 2 ) : 6 4 h + 1 6 k + 6 2 4 = 0
i.e., 4 h + k + 3 9 = 0 ⟶ ( 4 )
Solving ( 3 ) and ( 4 ) simultaneously we have, h = − 9 and k = − 3 .
Now,
f ( x ) = 2 x 4 − 9 x 3 − 3 x 2 + 3 4 x − 2 4
By long division, we have:
2 x 2 + x − 6 x 2 − 5 x + 4 ) 2 x 4 − 9 x 3 − 3 x 2 + 3 4 x − 2 4 2 x 4 − 1 0 x 3 + 8 x 2 x 3 − 1 1 x 2 + 3 4 x x 3 − 5 x 2 + 4 x − 6 x 2 + 3 0 x − 2 4 − 6 x 2 + 3 0 x − 2 4 0
∴ f ( x ) = ( x 2 − 5 x + 4 ) ( 2 x 2 + x − 6 ) = ( x − 1 ) ( x − 4 ) ( 2 x − 3 ) ( x + 2 )
Hello, I would pretty much appreciate if you guys can teach me how to do long division in LaTex. In my solution, I had to use mnay "\quad" s to allign my text as i want and it still looks horrible. Help is appreciated.
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You can use "\;" or "\," for shorter spacings
Let x^2 - 5x + 4=
f(a) = ( x - 1)(x - 4)
.We have to find the remaining 2 factors.
.In the given expression the first term is 2x^4.
.This 2x^4 is formed by product of x^2 of f(a) and the first term of remaining factor.
.Hence,the first term of remaining factor is 2x^2.
.By options we find that (2x - 3)(x + 2) gives 2x^2 as first term.
.Hence : (x - 1)(x - 4)(2x - 3)(x + 2)
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Let f ( x ) = 2 x 4 + h x 3 + k x 2 + 3 4 x − 2 4 . Since x 2 − 5 x + 4 = ( x − 1 ) ( x − 4 ) , This implies that:
{ f ( 1 ) = 2 + h + k + 3 4 − 2 4 = 0 f ( 4 ) = 5 1 2 + 6 4 h + 1 6 h + 1 3 6 − 2 4 = 0 ⟹ h + k = − 1 2 ⟹ 4 h + k = − 3 9 . . . ( 1 ) . . . ( 2 )
( 2 ) − ( 1 ) : 3 h ⟹ h ( 1 ) : ⟹ k = − 2 7 = − 9 = − 3
⟹ f ( x ) = 2 x 4 − 9 x 3 − 3 x 2 + 3 4 x − 2 4 = ( x 2 − 5 x + 4 ) ( 2 x 2 + x − 6 ) = ( x − 1 ) ( x − 4 ) ( 2 x − 3 ) ( x + 2 )