Question

The equation
x^2+ 3x = 94
has a solution between 8 and 9.
Use a trial and improvement method to find this solution.
Give your answer correct to 1 decimal place.
You must show all your working.
On the same line as your final answer you must write “to 1 decimal place".

Answer 1

Explanation:

Let's use a trial and improvement method to find this solution.

Step 1. Let's choose x = 8.5

Substituting into the equation:

$(8.5)^2+ 3(8.5) - 94=0? \\ \\ 72.25+25.5-94=0? \\ \\ 3.75\neq 0$

Step 2. Let's choose x = 8.4

Substituting into the equation:

$(8.4)^2+ 3(8.4) - 94=0? \\ \\ 70.56+25.2-94=0? \\ \\ 1.76\neq 0$

Step 3. Let's choose x = 8.3

Substituting into the equation:

$(8.3)^2+ 3(8.3) - 94=0? \\ \\ 68.89+24.9-94=0? \\ \\ -0.21\neq 0$

Since the sign of the equation changes from positive to negative when evaluating from 8.4 to 8.3, then x = 8.3 seems to be a reasonable value. Finally, the solution to 1 decimal place is:

$x=8.3$