Quadratic Equations and Inequalities: Practice and Methods
Solve quadratic inequalities by looking at the graph and the -axis: the discriminant tells you how many times they meet, and the graph shows where it is above or below.
Basic, Standard: Grade 10 · Term 2 / Advanced: Grade 12 · Exam prep
Math problem generator
The quadratic formula and discriminant
If the -coefficient is :
The sign of the discriminant gives the number of real roots (points where the graph meets the -axis): 2 if , 1 if (tangent), and 0 if .
Solving quadratic inequalities
If and has two real roots , then
If the coefficient is negative, multiply by first (reversing the inequality). If , complete the square: holds for all real numbers except 2, while only for .
Inequalities that always hold; location of roots
" for every real " means the upward parabola never meets the -axis, so . If the coefficient contains a parameter, check the case where it is 0 separately.
has two distinct positive roots exactly when
① ② the axis is positive ③ .
"One root greater than and the other less than " is simply .
Worked examples
Solve the quadratic equation.
Hint
Try to factor the left-hand side.
Answer
Solution
Factor the left-hand side.
Hence
Find the positive constant for which has a double root, and find that root.
- (1)The value of
- (2)The double root
Hint
A double root occurs when ; the double root is .
Answer
- (1)
- (2)
Solution
With discriminant ,
gives . Since ,
The double root is then
Find the range of the constant for which exactly 2 integers satisfy .
Hint
The left side factors as . Split into cases by comparing with .
Answer
Solution
Factoring the left side,
If , the solution is . The integer solutions are exactly when
If , the solution is . The integer solutions are exactly when
If there is no solution. Therefore
Practice problems
Solve the quadratic inequality.
Hint
Factor the left side and think about where the graph is above or below the -axis. If the coefficient is negative, multiply both sides by .
Answer
Solution
Factor the left-hand side.
The roots of are , so
Find the range of the constant for which has two distinct real solutions.
Hint
Use the sign of the discriminant. Since the -coefficient is , it is easier to use .
Answer
Solution
With discriminant ,
The condition is , so
Find the range of the constant for which the quadratic equation has two distinct negative solutions.
Hint
Let and describe where the graph meets the -axis using the discriminant, the axis, and the sign of at a point.
Answer
Solution
Let ; its graph opens upward with axis . The conditions are
The discriminant gives
The value at the point is
Combining the conditions,