Which statement about 4x2 + 19x – 5 is true? One of the factors is (x – 4). One of the factors is (4x + 1). One of the factors is (4x – 5). One of the factors is (x + 5).

Verified Answer :

\(4 x^{2} + 19x - 5 \\ \\ 4 x^{2} + 20x - x - 5 \\ \\ 4x(x + 5)-(x + 5) \\ \\ (x + 5)(4x - 1)\)

The answer is D) one of the factors of (x + 5). Why? 

(x - 4) is not one of the factors. 
(4x + 1) is not one of the factors.
(4x - 5) is not one of the factors.
(x + 5) IS one of the factors.

Answer:

Only "One of the factors is (x + 5)." is TRUE.


Step-by-step explanation:

  • What makes \((x-4)\) equal to 0?

\(x-4=0\\x=4\)

  • What makes \((4x+1)\) equal to 0?

\(4x+1=0\\4x=-1\\x=-\frac{1}{4}\)

  • What makes \((4x-5)\) equal to 0?

\(4x-5=0\\4x=5\\x=\frac{5}{4}\)

  • What makes \((x+5)\) equal to 0?

\(x+5=0\\x=-5\)


Note: Putting all those 4 values into the function \(4x^{2}+19x-5\), whichever value makes the function equal to 0, the corresponding expression would be considered a factor of the function \(4x^2+19x-5\).

  • Putting \(x=4\) into \(4x^{2}+19x-5\) gives us:

\(4(4)^{2}+19(4)-5\\=135\)

  • Putting \(x=-\frac{1}{4}\) into \(4x^{2}+19x-5\) gives us:

\(4(-\frac{1}{4})^{2}+19(-\frac{1}{4})-5\\=-\frac{19}{2}\)

  • Putting \(x=\frac{5}{4}\) into \(4x^{2}+19x-5\) gives us:

\(4(\frac{5}{4})^{2}+19(\frac{5}{4})-5\\=25\)

  • Putting \(x=-5\) into \(4x^{2}+19x-5\) gives us:

\(4(-5)^{2}+19(-5)-5\\=0\)


As we can see, only putting \(x=-5\) in the function gives us a value of 0. So the corresponding expression \((x+5)\) is a factor of the function.