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f(x)=(5x+3)(x-2)(3x+7)(x+5) has zeros at 
x=-5,x=-(7)/(3),x=-(3)/(5), and 
x=2.
What is the sign of 
f on the interval 
-(7)/(3) < x < -(3)/(5) ?
Choose 1 answer:
(A) 
f is always positive on the interval.
(B) 
f is always negative on the interval.
(C) 
f is sometimes positive and sometimes negative on the interval.

f(x)=(5x+3)(x2)(3x+7)(x+5) f(x)=(5 x+3)(x-2)(3 x+7)(x+5) has zeros at x=5,x=73,x=35 x=-5, x=-\frac{7}{3}, x=-\frac{3}{5} , and x=2 x=2 .\newlineWhat is the sign of f f on the interval \( -\frac{7}{3}

Full solution

Q. f(x)=(5x+3)(x2)(3x+7)(x+5) f(x)=(5 x+3)(x-2)(3 x+7)(x+5) has zeros at x=5,x=73,x=35 x=-5, x=-\frac{7}{3}, x=-\frac{3}{5} , and x=2 x=2 .\newlineWhat is the sign of f f on the interval 73<x<35 -\frac{7}{3}<x<-\frac{3}{5} ?\newlineChoose 11 answer:\newline(A) f f is always positive on the interval.\newline(B) f f is always negative on the interval.\newline(C) f f is sometimes positive and sometimes negative on the interval.
  1. Identify Zeros: f(x)f(x) has zeros at x=5x=-5, x=73x=\frac{-7}{3}, x=35x=\frac{-3}{5}, and x=2x=2. To determine the sign of f(x)f(x) on the interval \frac{-7}{3} < x < \frac{-3}{5}, we need to test a value within this interval.
  2. Choose Test Value: Choose a test value between 73-\frac{7}{3} and 35-\frac{3}{5}, let's pick x=1x=-1. Substitute x=1x=-1 into f(x)f(x) to determine the sign.
  3. Substitute and Determine Sign: f(1)=(5(1)+3)((1)2)(3(1)+7)((1)+5)=(2)(3)(4)(4)=96f(-1) = (5(-1)+3)((-1)-2)(3(-1)+7)((-1)+5) = (-2)(-3)(4)(4) = 96. Since 9696 is positive, f(x)f(x) is positive for our test value.
  4. Continuity and Sign: Since f(x)f(x) is a polynomial function, it is continuous and will not change sign between zeros unless it crosses a zero. There are no zeros of f(x)f(x) between 73-\frac{7}{3} and 35-\frac{3}{5}, so f(x)f(x) must be positive throughout this interval.

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