Answer:
Roots of the f(x) is -7 , 4 and 2.
Explanation:
Give that
5x^3-5x^2-170x+280 is (x+7)
One factor of f(x) = x + 7
So,
One root , x = -7
First we determine All factors of the given f(x).
Now divide f(x) by given factor the results are given below:
f(x) = ( x + 7 ) ( 5x² - 30x + 40 )
= ( x + 7 ) ( 5x² - 20x - 10x + 40 )
= ( x + 7 ) ( 5x( x - 4 ) - 10( x - 40 ) )
= ( x + 7 ) ( x - 4 ) ( 5x - 10 )
Now
Place x = -7 in the given function,
f(-7) = 5(-7)³ + 5(-7)² - 170(-7) + 280 = -1715 + 245 + 1190 + 280 = 0
So, First root is -7
Now, Place x = 4
f(4) = 5(4)³ + 5(4)² - 170(4) + 280 = 320 + 80 - 680 + 280 = 0
So, Second root is 4
ANd, place x = 10/5 = 2
f(2) = 5(2)³ + 5(2)² - 170(2) + 280 = 40 + 20 - 340 + 280 = 0
So, Third root is 2
Therefore, Roots of the f(x) is -7 , 4 and 2.