Answer:
k = 5/6
Step-by-step explanation:
First, we can make this have the form of a quadratic function, or ax²+bx+c=0. To do this, we can first subtract 10x from both sides to get
(2k+1)x²-8x=-6
Next, we can add 6 to both sides, resulting in
(2k+1)x²-8x+6 = 0
For a quadratic function of form ax²+bx+c=0, we can see that a=2k+1, b=-8, and c=6. We can then apply the quadratic equation, or
x= (-b ± √(b²-4ac))/(2a) to get our roots to be
x= (8 ± √(64-4(6)(2k+1)))/(2*(2k+1))
= (8 ± √(64-(48k+24)))/(4k+2)
= (8 ± √(40-48k))/(4k+2)
For the roots to be equal, we must have the two roots equal to each other. We can write this as
(8 + √(40-48k))/(4k+2) = (8 - √(40-48k))/(4k+2)
multiply both sides by (4k+2) to remove the denominator
8+√(40-48k) = 8 - √(40-48k)
subtract 8 from both sides to isolate the square roots
√(40-48k) = - √(40-48k)
The only number that is equal to its negative self (and is real) is 0. Therefore, √(40-48k) = - √(40-48k) = 0, so we have
√(40-48k) = 0
square both sides to remove the square root
40-48k = 0
add 48k to both sides to isolate the k and its coefficient
40 = 48k
divide both sides by 48 to isolate k
k = 40/48 = 5/6
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