Factoring quadratic trinomial is the expanding of it.
Example:
Given:4x2 + 7x – 15
Find the product ac:(4)(-15) = -60
Think of two factors of -60 that add up to 7:-5 and 12
Write the 7x as the sum of -5x and 12x:4x2 – 5x + 12x – 15
Group the two pairs of terms:(4x2 – 5x) + (12x – 15)
Remove common factors from each group:x(4x – 5) + 3(4x – 5)
Notice that the two quantities in parentheses are now identical.
That means we can factor out a common factor of (4x - 5):(4x – 5)(x + 3)
