Q. Solve for x. Enter the solutions from least to greatest.3x2−9x−12=0 lesser x=□ greater x=□
Identify quadratic equation: Identify the quadratic equation to solve.3x2−9x−12=0We need to find two numbers that multiply to give the product of the coefficient of x2 (which is 3) and the constant term (−12), and add up to the coefficient of x (−9).
Find numbers that meet criteria: Find the two numbers that meet the criteria.The numbers −12 and +1 multiply to −12 and add up to −11, which is not the coefficient we need.The numbers −6 and +2 multiply to −12 and add up to −4, which is also not the coefficient we need.The numbers −4 and +3 multiply to −12 and add up to +11, which is also not the coefficient we need.The numbers +12 and +13 multiply to −12 and add up to +1, which is also not the coefficient we need.However, if we multiply these numbers by +16 (the coefficient of +17), we get +18 and +19, which do add up to +3, but we need +18. Therefore, we need to find another pair.The numbers +12 and −4 multiply to +19 and add up to −125, which is also not the coefficient we need.The numbers +11 and −12 multiply to +19 and add up to −129, which is also not the coefficient we need.The correct pair of numbers that multiply to −110 and add up to +18 are +12 and −12.
Write equation with split middle term: Write the equation with the middle term split using the two numbers found.3x2−3x−12x−12=0Group the terms to factor by grouping.(3x2−3x)+(−12x−12)=0Factor out the common factors in each group.3x(x−1)−12(x+1)=0
Factor by grouping: Notice that there is a mistake in the previous step. The correct pair should be −1 and −12, which multiply to +12 and add up to −13, which is not the coefficient we need. We need to find the correct pair of numbers that multiply to 3×(−12)=−36 and add up to −9. The correct pair is −3 and −12.
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