SOLUTION: Use algrebra so solve (x-1)(x+2)=18 iv tried and failed please help me :)

Question 226036: Use algrebra so solve (x-1)(x+2)=18
iv tried and failed please help me :)
Answer by drj(1380) (Show Source): You can put this solution on YOUR website!
Use algebra so solve (x-1)(x+2)=18

Step 1. Multiply out to get rid of the parenthesis.

Step 2. Subtract 18 from both sides of the equation

and or and

Step 4. We can also solve using the quadratic equation shown below:

where a=1, b=1 and c=-20

Solved by pluggable solver: SOLVE quadratic equation with variable

Quadratic equation (in our case ) has the following solutons:

For these solutions to exist, the discriminant should not be a negative number.

First, we need to compute the discriminant : .

Discriminant d=81 is greater than zero. That means that there are two solutions: .

Quadratic expression can be factored:

Again, the answer is: 4, -5. Here's your graph:

...same as before.

Step 5. ANSWER: The solutions are x=-5 and x=4.

I hope the above steps were helpful.

For FREE Step-By-Step videos in Introduction to Algebra, please visit http://www.FreedomUniversity.TV/courses/IntroAlgebra and for Trigonometry visit http://www.FreedomUniversity.TV/courses/Trigonometry.

Good luck in your studies!

Respectfully,
Dr J
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