`y = (4x + 9)(4x - 9)` Write the quadratic function in standard form.

Expert Answers
labellavita89 eNotes educator| Certified Educator


To get this quadratic function in standard form we need to use a distribution method called FOIL. FOIL stands for First, Outer, Inner, Last. This is a way to keep yourself organized in distributing each number. 

Step 1: Multiply the First terms in each parentheses

            `4x * 4x = 16x^2`

Step 2: Multiply the Outer terms

            `4x * -9 = -36x`

Step 3: Multiply the Inner terms

            `9*4x = 36x`           

Step 4: Multiply the Last terms in each parentheses

             `9*-9 = -81`

Step 5: Now put the solutions together

           `y=16x^2 -36x +36x -81`

Step 6: Combine like terms

          `y=16x^2 -81`

shmindle | Student

We can use the foil method to solve this equation.

First: `(4x)(4x)=16x^2`

outside: `(4x)(9)=36x`

Inside: `(4x)(-9)=-36x`

Last: `(9)(-9)=-81`

All together: `16x^2+36x-36x-81`

` =16x^2-81`

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