Question

One of the solutions to the equation 5x^2+bx+12=0 is − 4/5. Find the other solution.

Answer 1

b=-19

Explanation:

We know that one of the solutions is x=-4/5

That is a solution to x. So if we plug in (-4/5) into the x in the equation, then it should equal 0.

5(-4/5)^2+b(4/5)+12=0

Now, just solve for b.

5(16/25)+b(4/5)+12=0

(16/5)+(4/5)b+12=0

(76/5)+(4/5)b=0

(4/5)b=-(76/5)

b=-19

Answer 2

x=-3

Explanation:

Using Vieta's theorem (X1+X2=-b/a, X1 * X2=c/a), we can plug in the values to create:

-4/5 * x = 2.4 <- (I got this by dividing 12 by 5)

Multiply both sides by 5 to get -4x=12, and divide by -3.

x = -3