Question

Find the value of q for which the equation

qx² - 6x + 18 = 0
has one repeated real root
q = ______

Answer 1

q =
`(1)/(2)`

Explanation:

given a quadratic equation in standard form

ax² + bx + c = 0 ( a ≠ 0 )

then the nature of the roots can be found using the discriminant

Δ = b² - 4ac

• if b² - 4ac > 0 then roots are real and irrational

• if b² - 4ac = 0 then the roots are real and equal

• if b² - 4ac < 0 then the roots are not real

qx² - 6x + 18 = 0 ← is in standard form

with a = q , b = - 5 , c = 18

for one repeated (equal) real root , then

b² - 4ac = 0 ( substitute values )

(- 6)² - (4 × q × 18) = 0

36 - 72q = 0 ( subtract 36 from both sides )

- 72q = - 36 ( divide both sides by - 72 )

q =
`(-36)/(-72)` =
`(1)/(2)`