The discriminantEdexcel International A Level Maths: Flashcards

What these 12 flashcards ask

What is the discriminant of ax^2+bx+c?
What does b^2-4ac0 tell you?
What does b^2-4ac=0 tell you?
What does b^2-4ac<0 tell you?
Condition for 'real roots' (distinct or equal)?
Value of the repeated root when b^2-4ac=0?
Discriminant of x^2-4x+7 and what it shows?
If b^2-4ac<0 and a0, where is the graph?
If b^2-4ac<0 and a<0, where is the graph?
x^2+kx+9=0 has equal roots and k0. Find k.
How do you test whether a line meets a curve?
Why must you exclude k=0 in kx^2+4x+(k-3)=0?

Exam questions on The discriminant

Consider the equation $x^2-4x+7=0$ .
Explain what the value of the discriminant tells you about the graph of $y=x^2-4x+7$ .2 marks
The equation $x^2+kx+9=0$ , where $k$ is a positive constant, has equal roots.
Solve $x^2+kx+9=0$ for this value of $k$ .2 marks
The line $y=2x+c$ and the curve $y=x^2-3x+4$ , where $c$ is a constant.
Show that the $x$ -coordinates of any points where the line meets the curve satisfy $x^2-5x+(4-c)=0$ , and show that the discriminant of this equation is $4c+9$ .3 marks

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).