Question

If x² – 8x – 9 = 0; values of x correct to one significant figure are ______.

Options

• 9 and – 1

• 9 or – 1

• 9.0 and – 1.0

• 9.00 or – 1.00

Answer 1

If x² – 8x – 9 = 0; values of x correct to one significant figure are 9 or – 1.

Explanation:

Given quadratic equation be,

x² – 8x – 9 = 0   ...(1)

On comparing equation (1) with

ax² + bx + c = 0

We have, a = 1; b = – 8 and c = – 9

Then by quadratic formula,

`x = (-b ± sqrt(b^2 - 4ac))/(2a)`

= `(-(-8) ± sqrt((-8)^2 - 4 xx 1 xx (-9)))/(2 xx 1)`

= `(8 ± sqrt(64 + 36))/2`

= `(8 ± sqrt(100))/2`

= `(8 ± 10)/2`

= `(8 + 10)/2` or `(8 - 10)/2`

= 9 or – 1