Find the positive and negative domains of the following function:
y=−2x2+3x+2
To solve the given problem, we will perform the following steps:
- Calculate the roots of the quadratic equation y=−2x2+3x+2 using the quadratic formula: x=2a−b±b2−4ac.
- Given a=−2, b=3, and c=2, use the formula:
x=2(−2)−3±32−4(−2)(2)=−4−3±9+16=−4−3±25
- The roots are x=−4−3+5=−21 and x=−4−3−5=2.
- The roots −21 and 2 divide the x-axis into three intervals: (−∞,−21), (−21,2), and (2,∞).
- Test a point from each interval in the function to determine the sign of the function in those intervals:
Choose x=−1 for interval (−∞,−21):
Substitute into the function: y=−2(−1)2+3(−1)+2=−2−3+2=−3 (negative).
Choose x=0 for interval (−21,2):
Substitute into the function: y=−2(0)2+3(0)+2=2 (positive).
Choose x=3 for interval (2,∞):
Substitute into the function: y=−2(3)2+3(3)+2=−18+9+2=−7 (negative).
Therefore, the positive domain where the function is positive is −21<x<2, and the negative domains are x<−21 or x>2.
The solution to the problem is:
x>0:−21<x<2
x>2 or x<0:x<−21
x > 0 : -\frac{1}{2} < x < 2
x > 2 or x < 0 : x < -\frac{1}{2}