Identify Factors for AC Method: We need to factor the quadratic equation4x2−43x−15=0. To do this, we will use the AC method, where A is the coefficient of x2, B is the coefficient of x, and C is the constant term. We need to find two numbers that multiply to A⋅C (4⋅(−15)=−60) and add up to B (−43).
List Factor Pairs: List the pairs of factors of −60 that could add up to −43. The pairs are (1,−60), (−1,60), (2,−30), (−2,30), (3,−20), (−3,20), (4,−15), (−4,15), −430, −431, −432, −433.
Find Correct Pair: Identify the correct pair of factors that add up to −43. The pair is (−48,5) because −48+5=−43.
Rewrite Middle Term: Rewrite the middle term of the quadratic equation using the pair of factors found in the previous step. The equation becomes 4x2−48x+5x−15=0.
Factor by Grouping: Factor by grouping. Group the first two terms and the last two terms separately. (4x2−48x)+(5x−15)=0.
Factor out Common Factor: Factor out the greatest common factor from each group. 4x(x−12)+5(x−3)=0.
Correct Mistake: Notice that the terms in the parentheses are not the same, which means there is a mistake. We need to find a different pair of factors of −60 that add up to −43. The correct pair is (−45,4) because −45+4=−43. We need to go back and correct the mistake.